There have been many times, over the years, that various wrestling promotions dropped the ball with an angle or a particular wrestler. Here, I'll mention some of them and give my take (which will likely include some fantasy booking).
The Four Horsemen in 1995/96.
In late 1995, the Horsemen were reformed, once again, with Flair, Anderson, Pillman and Chris Benoit. They did alright, as Flair won the World Title from Randy Savage, a couple times. However, the feud with the Dungeon of Doom just seemed lame and pointless. Once Pillman left WCW, they had a chance to bring in someone that would have fit in, perfectly; Dean Malenko. He'd already been teaming with Benoit in ECW and when they arrived in WCW. He had the mentality and the reputation to blend in (which he did, in 1998). Benoit and Malenko could have been World Tag Team Champions in early 1996, bringing more gold to the Horsemen. They worked very well together and, later on, Malenko's Cruiserweight Title reigns could have meant more success for the Horsemen. Instead, they chose an ex-football player, Steve McMichael. This guy sucked, in every possible way. Malenko was the natural choice. Furthermore, the Horsemen had until Bash at the Beach and the birth of the nWo to be the top heels in the company. Had they been built up more, earlier in the year, they might have seemed like more of a threat when time came to defend WCW. By late 1998, when they brought the Horsemen back (with Malenko), they still didn't get behind them the way that they should have. Flair was in charge of things and had the World Title, yet his own stablemates were treating like garbage so he could align himself with...DDP? WCW dropped the ball with the Four Horsemen, like many times before.
Hogan v. Sting, Starrcade 1997.
This was, possibly, the most highly anticipated match in WCW history. Bischoff did very well with this, as the angle built up for a year and a half. This should have been the moment for WCW to, finally, get a big win against the nWo. However, this was ruined long before Starrcade happened. Hogan's title loss to Lex Luger took a lot of steam out of this, as Luger became the man to draw first blood against the nWo, and he did so in a rather meaningless fashion, dropping the belt back a short time later. As for the Hogan-Sting match, itself, this was the beginning of the end for WCW. Instead of Sting getting the big win over Hogan, he was pinned cleanly. To make matters worse, Bret Hart then demands that the match be restarted, more or less, screwing Hogan out of the title. I think, without the Hart element, they wouldn't have even attempted to claim a fast count for Hogan and things would have gone as they should have. People cite the Fingerpoke of Doom as the moment when the WCW World Title became meaningless, but I think it lost a lot of credibility as a result of Starrcade 1997. This leads into my next issue...
Bret Hart in WCW.
After the infamous Montreal Screwjob, "The Hitman" was hotter than ever. What better way to introduce him to WCW fans than by making him a guest referee. They did practically nothing with him, finally giving him the World Title after he'd been there for two years. Bret Hart should have been exploited as the hot commodity that he was. They were certainly paying enough for him. He should have come in and led the charge against the nWo (knowing that there was no chance he'd be able to just do his own thing on the side). They could have worked an angle, through most of 1998, where "The Hitman" pursued Hogan and then, finally, got his chance and took him out. This would have been the big blow needed to cripple the nWo and pave the way for something new. Instead, he was turned from face to heel and back, way too much. While Goldberg (a rookie) got a massive push and a World Title run, Hart was doing well to even keep the U.S. Title. It's not as if he was washed up or had been gone for a while. He left WWF as the champion, as far as most are concerned. They didn't need to build him up because the whole wrestling world was talking about him, already. Bischoff and Co. truly failed on this one.
After Sting beat Hogan, WCW should've immediately had Bret Hart challenge Sting for the World Title. This would've been (just like with Flair and Hogan back in 1991-1992) a perfect opportunity to promote a WCW Champion v. WWF Champion (since it could be argued that Bret never actually lost the title to Shawn Michaels at Survivor Series) match down the road. However, WCW screwing up Hogan v. Sting was the beginning of the end for WCW. They had the WWF in position to drop the final nail but, they never really recovered after 16 months of building him up as the guy, only to have him not win clean against Hogan. Adding on top of this, Bret should have came in and immediatly been a WCW tradition guy and been the catalyst in the death of the nWo. The money that WCW blew by not only not having Sting beat Hogan clean.....but never even having a Hart/Hogan feud, let alone a match on a PPV is completely ricockulous.
Mike Awesome defects to WCW.
With all the controversy surrounding Awesome, WCW could have capitalized and really pushed him. The WCW World Title was already being tossed around to anyone with a heartbeat, so it's not like they had big plans for it. They wasted so much time pushing Booker T as the poor man's Rock, yet blew a chance to push Awesome to the moon.
Raven in TNA.
In early 2003, Raven left WWE and joined TNA. In many ways, he seemed to really put them on the map. I know several people that only began watching TNA because Raven joined and they were waiting for him to get the NWA World Title. He was red hot and it seemed that, during 2003, his career was resurrected. Things had been winding down for him, since his second stint in ECW, yet it felt as if he'd been 'reborn' upon gaining his freedom from Stamford. He was insanely over with the crowd. I was in the building, one night, as he challenged AJ Styles for the title, and the whole building was ready to explode just as soon as he won the match. The support for Raven was deafening and there was a wave of disappointment as he was screwed over.
In 2005, when TNA no longer even had a TV show, then they put the title on Raven. There was no real build to it, other than the fact that he'd been talking about it for two years. It seemed that TNA did that for the sole purpose of keeping fans interested while they were off the air, since it was common knowledge that Raven had a huge fanbase online and would go the extra mile to keep up with things. Once they got a TV deal again, they screwed him out of the belt and put it back on Jarrett. Due to his deteriorating health, Raven wasn't anywhere near the title after that and has since left TNA. What a waste.
The Lex Express
Lex Luger received a massive face push, in the summer of 1993. He was the first man to bodyslam Yokozuna and secured a WWF Title shot at Summerslam. For some reason, WWF failed to really get behind his push and gave him a lame count out victory, at the PPV. It was from this point on that Luger was considered damaged goods. WWF dropped the ball by not putting the belt on Luger, at Summerslam 1993, and they did a lot of damage to his career as well. Certainly, he was no Hulk Hogan. He'd already come off as a poor man's Hogan, in WCW. But once things got moving, they should have gone with it. It would have been quite easy to turn him heel and have him work a feud with Bret Hart. Anyone that saw Luger's WCW World Title reign, back in 91-92, already knew he'd make a decent heel. He could have even, blatantly, come out and said that the whole red, white and blue thing was just an act to get the title shot. A child could have written a decent storyline for him. After promoting the hell out of him, especially with the Lex Express Tour, they dropped the ball by not capitalizing on it.
Vader in WWF.
Vader dominated WCW, in the early 90s. At one point, he held titles in Europe, Japan and North America. He was the epitome of monster heel. When he arrived in WWF, most people expected big things. He lost a bit of steam, in WCW, since Hogan totally no-sold his devastating powerbomb. Still, WWF could have easily re-established him as an unstoppable monster. Instead, he debuts by attacking Gorilla Monsoon and gets suspended. Then they waste time putting him in matches with Yokozuna, when he should have been taking out people like Shawn Michaels, Razor Ramon and Bret Hart. HBK should have dropped the WWF Title to Vader, without a doubt. A Vader-Hart feud, after that, would have been epic. He still had several good years left in him, yet they jobbed him out and neutered him. Major 'drop the ball" moment for WWF.
There are many more examples, but this is enough for now.