Strong disagreement. The acquisition happened in 2006. The last few great Pixar movies were in the pipeline already (Ratatouille - 2007, WALL-E - 2008, Up - 2009).
I disagree too from a animation/story-quality perspective, but from a business perspective, Pixar seems to be doing well enough to meet OPs criteria of not being ruined.
Lightyear was a letdown. My kids enjoyed it but I thought it could have been much better. I expected to see Buzz as at this exciting space ranger, but that wasn't what the movie was about. If I was Andy from Toy Story there would be no way I wanted a Buzz toy after seeing that movie.
Ah. Might have to watch it then. After a number of duds I gave up on watching new Pixar movies except for those made by Brad Bird, or especially recommended.
I'd argue the only real misses were the cash grab sequels (Cars 2, Cars 3, and I can only assume Lightyear is in that group but looking at RT it seems like both ratings are still "fresh"). The rest of the movies on the post-acquisition list were good, if not great. Critically, I think the worst one on the list is the Good Dinosaur and even that's still generally well liked.
Cars 2 was the only real stinker. I agree they're not 100% excellent, but most are at least okay. And from your list: Brave, Cars 3, Coco, Onward, Luca, and Turning Red I all consider great to excellent. I haven't seen Lightyear yet.