Was Brilliance II released too late? So that people didn't really get into it, thus not being as nostalgic about it, before the fall of the Amiga?
I think you got it. Brilliance 2 was damn near perfection on a 15khz screen. But I think that it was introduced around the time of the C= bankruptcy or maybe even after it. The Amiga was already well into its slide out of the mainstream.
The only edge I can give to DPaint is that IIRC, Dpaint V handled RTG and mode promoted screens a bit better. I remember having some quirks trying to use a 640x400 DblNTSC screen in Brill 2. (And I didn't buy that Sony 15/30 MultiSync monitor just so I could have blinding flickering in my paint program! ;-) )