Reading a few things here and there, it would seem that things were blown out of proportion as to how he reacted to this negativity and was well-aware that there were tons of fans out there who appreciated him.
Seems the man had many reasons to cease performing, including health related issues.
As for Gallagher vs Collins, I appreciate both. Gallagher is a good songwriter and an adequate singer, and that's it. I watched 2 minutes of interview w/ him recently and felt like slapping him in the back of the head. So whether it's him or Collins, I'd rather focus on their music.
Collins is 100 times the musician Gallagher is. Sure, some parts of his catalogue haven't aged all that well - but that's a fraction of the man's artistic output. You may be embarrassed when you hear Sussudio or intensely dislike other parts of his catalogue but still appreciate what he did with Genesis. You could dislike his songs but still appreciate his drumming.
Whereas with Gallagher, if you don't like the Beatles, there are big chances that you won't like anything he wrote...