What was his finest moment, /mu/? Was it Comfortably Numb?
It's Time. Yes, Comfortably Numb is a great example of virtuosity and improvisation (especially live), but Gilmour's value as a guitarist was always his sense of phrasing, pacing, and building drama, and Time's solo is a master class in all of those. It's got a distinctly memorable beginning, middle, and end and complements the song perfectly.
No. People love to overexaggerated how much of a dictator Rog was over the band. Even if you consider Animals to be a Roger album, Dogs was pretty much Gilmour's song on the album. Gilmour's albums were obviously the ones after Roger left, and anything before Animals mostly collaboration between them all (Nick not all that much though.)