I can make a lot of examples of people who were recently released in the past two years, and some who have faded into being on Main Event. But one I will say which isn't the worst run per-say, but has missed a lot of potential.
Shinsuke Nakamura.
There is a language barrier with him which is a challenge, but it is possible for foreign stars to overcome it as we have seen with Asuka (even if she has had her hiccups also).
But here he is, someone known for wrestling a unique style, having an ungodly charisma which expands beyond language barrier, unique look, and has already earned a reputation elsewhere of being an international star. In NXT it was mostly good, had a near-perfect debut, beating Sami Zayn in a MOTY contender, and was a two-time NXT Champion. On the main roster, he had a hyped post-mania debut, but things never clicked fully and a lot of it has to do with WWE's booking. His debut at Backlash really should have either been two things. 1. A dominant win or 2. A match where he could do his thing. His match with Ziggler was alright... but was a bog standard WWE match falling the same template which doesn't suit Nakamura.
Then over the year he had a mixed bag, some good, some so-so, and he won the rumble. We were getting him vs Styles, arguably the match which truly made WWE want to sign him but this time at Mania for the WWE title. The match at Mania was pretty good overall, but with a dead crowd as part of WWE's always overly long manias and the story building to it lacking that extra sizzle to make it big, it didn't have as much heat. Then the heel turn, hey, maybe we'll get the King of Strong Style as a heel? And he spends an entire feud knocking AJ Styles in the balls and loses.
Ever since, he has had some good matches, but his star has faded greatly. Honestly, I forgot he was IC Champion half the time during his reigns because despite the fact he showed in Japan if you give him a mid-card belt and let him go, he can raise it to world title standards, they refused to give him anything and he didn't even defend the title most the time, preventing him from doing what got him signed in the first place, you are losing out.
Him losing his WWE title feud was not the end of him, but it certainly gave a bad sign which has been mostly right. He won a Royal Rumble, Shinsuke won some titles. US Title, IC... and hold up *checks wiki* HE HAD A TAG TITLE RUN TOO!? But this guy who was an absolute star, him along with Tanahashi helped bring New Japan out of its darkest era and paved the way for a renaissance, a new golden age that arguably ended once the pandemic hit but the company still remains strong, and you sign him and... he doesn't feel special anymore. Even if not everyone can be in the main event forever, with him having English as his second language (though he has gotten better over the years) you have a limitation, but you have shown yourself willing to book around stuff like that (stuff like a manager) and make stars. He could have had at least one run on top as a charismatic champion, give him a couple good feuds with people he can have great matches with, then once he drops the belt, even if he goes down the card, he can still be a reliable guy to put on enjoyable matches, pop the crowd with one of the best entrances ever, and have a hint of a special aura about him and be capable of going to the main event again when needed. That though, may have been lost.
The saving grace is at least Shinsuke has earned himself a nice pay-day during his run. He's earned it.
Now to make it more positive, let's listen to his amazing theme songs.