I simply don't like how Oda made her. Sure as hell I don't like at all that "I'm Oden" metal disorder, more so when she said it in front of Oden's orphan son. Also, Oda made sure to have her suck up Ace randomly, which is another no.
she was forced into imprisonment since she was a child and forced to fight her father for 20 years, all she had to cling to was Odens diary which came from a deep admiration & desperation for freedom. If you actually read the manga she took on Odens persona to emulate his spirit & goals. Overall it was a coping mechanism.
not sure if you know this but Oda is an actual genius and doesnt just make everything surface level
She isn't also part of the plot in any way: she randomly pop up at some point and starts doing things: at least, made her part of Kaido's actions and have her redeem herself down the line.
every person just randomly pops up at some point and starts randomly doing things lol
Yamato was introduced before "she popped up" Kaido was searching for her and she took her own path and was able to help fulfil one of Odens goals, liberating Wano.
what exactly did she have to redeem herself from?
About her role, obv. the arc would have changed. It would have been nice, for example, instead of having the Scrabbards randomly go against Kaido before and being clapped (as obvious: they already knew they were no match), use them to buy time against him instead of Yamato. And possibly even prevent the island from exploding after.
the arc would have changed with the alliance losing.
randomly went against kaido, not sure what is at all random about it, like at least please read the manga before complaining lol
not sure if you know this but for most of the scabbards they've held a 20 year grudge and were over confident in their new found strength. did they get handled incorrectly possibly yes, they shouldve been the ones to actually kill kaido and orochi, but no they all combined would have been unable to fight hybrid kaido for over 15-20 minutes strength whil also effectively wearing him down and physically hurting him and knocking him down.