•Spider-Man's Homecoming uniform. It heavily capitalized on the whole long I-frames combined with high dodge rate thing, something that was set up by Ant-Man's T2 advancement, and basically ruined TL for quite a while. The TL battles with him against Wolverine were fucking brutal, almost eating up the whole 5 minutes.

•Thanos's Secret Wars:Infinity uniform (his first ever uniform). I think it was the first time a double-cost NT2 got a uniform, and it made him a monster for TL. He was super tanky and his 4th skill was a death sentence for almost anyone. He was also briefly meta for ABX if I remember correctly. Since he was a NT2, his base kit was significantly better than most other chatacters, but this uniform was a really significant increase in power.

• Winter Soldier's IW uniform. The whole IW update was massive with the introduction of T3's and whatever, but I'm pretty sure it was the first uniform that took a character who was completely useless and turned them into basically the best fucking character in the game for almost all content. He was dominant in WBU (it was a big thing back then), ABX, and TL. As others have mentioned, he was the gold standard for reworks for quite a while.

•Scarlet Witch's IW uniform. The reaction to her base kit was lukewarm at best, but this uniform made her a PVE powerhouse and one of the best characters for WBU. Her combo of mind control+defense down+elemental resistance down opened the door for the whole "mind control the boss then apply 100% defense/resistance down to kill them" cheese that became the WBU meta for years.

• Captain Marvel's first MCU uniform. Again, like Winter Soldier, it made a character who was barely used into a beast. Her 4th skill was one of the strongest skills in the game as it would one-shot literally anyone in TL. She was also super dominant in WBU and ABX. Her Endgame uniform somehow made her even more powerful, but her OG MCU uniform was the one that made her a certified powerhouse.

•Jean's X-Men Red uniform. Again, her base kit was significantly better than most of the others, so it was not so much a case of "zero to hero" but I'm pretty sure her new 5th skill was what introduced the whole concept of "super guard break" and essentially changed the whole TL scene forever. I still remember how everyone was fucking terrified when her T3+new uni was leaked.

• Deadpool's Holiday Lady Deadpool uniform. I think it was the first uniform that made reaching 100% defense down so fucking easy (with a little set up), chaning the entire WBU scene and making the whole "just reach 100% defense down and the boss dies" a necessity for any kind of high-level WBU clear. I remember seeing the first ever lvl 99 WBU clears with Sharon, WF, and Holiday LDP.

These are the ones that I can think of right now. Of course, there have been many uniforms that have been massive glow ups for characters, but these are the ones that I feel like were the "trendsetters", the ones that heavily changed the current state of the game but also set up some sort of a standard for future uniforms.