I've never heard any of my straight edge friends say that it's necessary for an artist to use drugs to provide inspiration for their craft. I have, however, heard this from many of my drug addict friends, many times over the years.
I infer from this several things (and this insight is coming from personal experience, as a struggling addict for several decades). There is usually some form of self-loathing, or at least, a lack of self-worth involved with recurring drug/alcohol use. For me personally, it was quite easy to relate to someone like Trent who was clearly suffering many of the same pains and thoughts felt by many of his fans, especially in TDS era. I think it's easy to assume that perhaps, as an addict, you can keep your shit together because it appears that someone like Trent is clearly keeping his shit together. Of course, in retrospect, it's quite obvious knowing that he had to be revived on an operating table from an overdose that he was far from having his shit together.
He was very, very lucky. I'm glad that he took control of his second chance and pushed his life in a different direction. There would have been no awards for Trent, no beautiful family, and no more great music for all of us to enjoy. I think it's tough for some fans that still struggle with addiction and/or thoughts of self-worth to see a different version of Trent ("I've survived everything...") that is now thriving. Perhaps an upbeat lyric or beat is tough to relate to when the previous version of him offered some sort of vindication to the self-destructive lifestyle a fan might choose for themself.
When I read fan comments like the one you refer to, such as Trent (or substitute any other artist here) was better when he was fucked out of his mind on drugs, screaming about suicide, I find the comment more self-reflective to the poster than to Trent's current artistic output.
Of course, one likes the music one likes and I'm not trying to offend anyone that has made comments like this before, because I'm someone that has personally said the same thing. I'm just giving my two cents from someone that has walked this road. Personally, I find more inspiration in the new Trent compared to the old Trent.
I'm glad David Bowie knocked some truth into him about not needing drugs to cope. (And anyone that knows anything about Bowie knows that he walked down that road to self-destruction too.) So personally, I love his new ode to Bowie, because I know he was one of the most important people in his life.