Writers can certainly change voice, but how much is debatable. I think I can change mine, but I also think there is a base pattern to my voice. For good or ill, I have voice, LOL.
Using voice as a “judge” for writing is dangerous, you can miss some great stuff. I tend to find I need to give an author fifty+ pages if their “voice” is much different from something I was reading previous. This makes critiquing short samples difficult, and why I never take comments on voice seriously unless someone has read a lot of pages.
Now, crappy writing is something else entirely. Crap writing can be an instant judgment, LOL.
I should also note I once changed voice enough switching to a different character that my editor told to me cut it out, so I backed off, LOL.
YMMV but I've found it by far the most reliable guide I know. I very rarely enthuse about the times I decide to try and force my way past an annoying voice and even less rarely regret the times I read stories based on voice alone.
Besides, everyone's gonna miss some great stuff come what may - simply not enough time to get it all. As long as its place gets taken by something else great, I find it best not to worry about it.
I also think its best to talk about change as a spectrum rather than a binary thing. I think pretty much every writer can throw their voice at least a little while still feeling natural, particularly those who write multiple characters in close PoVs. The question is how much they can throw it. Tom Holt seems to have an astounding range. David Eddings seems to have an incredibly narrow one, although maybe I wouldn't think that if I'd read High Hunt.