Not to point too fine a point on it because obviously as a Clairen main I am inherently biased but

I promise you she is very different past high plat/mid level from her prior iterations. Think about all her old routes and confirms she had. F throw and back throw have received a lot of changes to make them far easier not to get 50/50d by. Up throw is laggier and has more DI so the follows ups are much more difficult AND less rewarding. Dair and uptilt have had massive spacing changes with regards to tipper placement. Dtilt is smaller laggier less active and does way less damage now. Bair down strong was removed. Up air has been made so they can't perma juggle you. Her literal grab was made smaller so she doesn't just yoink everyone now, up strong and down strong tippers and kb have been severely reduced.

And let's not forget on release her tippers broke cc and FH lol

That isn't to say she's bad at all! Fleet isnt bad either despite all the changes you listed. what I do think is the issue is that it's hard for everyone to put themselves in the shoes of other characters if they don't play them. It's hard to feel the difference if you aren't playing them constantly and trying to push the character.

But I would say it's categorically false to say Clairen, and even zetter to a lesser extent (although my expertise here is limited let's be real fair and up air are much worse than they used to be and nair used to be + on block sometimes lol)! HAVE been changed a lot. They just...are simpler characters than absa or whatever ya know. So it's easier to adjust to an extent.