I don't care all that much about Ki Adi but he has his fans and is an established character, a good guy. This show just insulted his fans (and the established lore) by retconning him not just in terms of age (having him be a midfle aged dude long before he was even born) but making him either super incompetent or evil for covering up the whole dark sider killing jedi thing and later stating Sith extinct and not mentioning any other type of darksider when Maul showed up.
Fans of the character and the established canon are right to be pi**ed off, because the show runners actively inserted a character who shouldn't be there just so they could character assassinate him like they did Han, Luke, Leia, Kenobi, Boba etc etc etc before. All Lucas era characters seem to be on the chopping block in service of artificially making Disney's creations look better.
I see it not as a tiny problem in a show full of problems but more as the 3rd straw in a row that broke the camels back. The show is full of issues and crackling campfires and retcon Ki Adi are emblematic of just how little care went into this show and its writing. They are like memes in that way, no text needed, just an image of the campfire or an image of young Ki Adi in high republic robes looking all shifty tell you everything you need to know about the people writing this mess.
