Uryu still did better than Renji at that point. Mayuri came in later with prep time and a counter to Szayel's powers.
define better?
A captain is a captain, they need to be able to show that they are able to at least be a certain strength or quality to attain that position. Whether he got a temporary boost or not, he still won. You can call it plot driven, but that would be for all the powers shown later on.
& mayuri did showcase that in sheer reiatsu where Uryu realized he was significantly weaker and couldnt beat him then found out mayuri was partially responsible for his grandfather and quincy purge which then went onto release once again a forbidden ancient weapon/technique that once use you lose all of your own powers following, Uryu had to pour out power, speed and strength that wasnt his and put everything into getting one phyiscal alt that bypassed hisghogijizou and was what beat mayuri, physical power which we all know he is possibly one of the phyiscally weakest captains. & no one actually won that fight, like i said Mayuri was fine after the blast with a hole in his chest due to his own abilities and was fine shortly after Uryu was left for dead after being fatally poisoned and nemu just randomly gave him the antidote... up until lets was released he was outclassed in every aspect..
not really cause uryu never had a "captain"-liek showing following that, HM was evident and proof that eveb after new found powers and training from his father that he was still just ats best LT level. this is a much stronger version than the one that fought mayuri on SS. why do you think it was that uryu didnt run into any other captain than being faced with the physically weakest on SS?
cause he wouldve lost by sheer physical force and unlike mayuri none of the other captains wouldve toyed around and antagonized him.
Blut and Sklaverei are natural quincy techniques, he had his schrift before Yhwach, but never unlocked it. He wasn't given these powers, he only had them unlocked.
The only thing he was given were amps from aushwalen which did help him get stronger.
Renji getting a "real" bankai can also be argued to be a plot-driven power since he was always taking L's most of the series.
Renji:
Lost to Byakuya
Lost to Szayellaporo
Lost to As Nodt (small confrontation)
yet they are all only awakened through Ywach and the schrift isnt assured it is what ywach deems is right for each character.
not really renji was constantly in a battle with his own bankai this goes back to SS against Byakuya.
So Renji only lost to characters that were actaully stronger than him and he didnt win absed off of plot driven storylines thanks for confirming this for us.
uryu us trash