I call BS, the amount of bugs I regularly run into I don't think they test much of anything. I sometimes wonder if they even use their own products. The current mini player regularly bugs out for me plus I run into general bugs in the YouTube app pretty often. I guess nobody gets promoted at Google for fixing bugs.
Same for Discord etc. There are tons of bugs and stupid design choices that reside for weeks. Meanwhile yes, Eternity (Lemmy client) Nightly does crash currently while commenting - so I'm using Eternity stable release - but that's probably already fixed and I just didn't update.