You're knowledge on that matter seems a little outdated, i guess. Gradients and Colour have no impact on
texture quality nowadays, even when dynamic. (GW2 is static, btw)
It would be impossible without the tech in WoW's old engine for sure...but GW2 for example doesn't look
oversaturated because of technical problems, but thanks to Art Direction (Sylvari Design for Reference)
Soloing old Content could be connected to searching and looting Dyes. The variation of Gearsets through difficulties
are no biggie imo: the sets are designed with the "Normal/Flex" Colouration in mind and it horribly shows sometimes...
some so called "Heroic" Gear often looks alot less epic like the normal variant, simply because the Colouration doesn't fit the Design necessarily. They brute-force it sometimes really. (And i never, ever heard of anyone in my years of heroic raiding that someone connected the tier-colour with prestige: mostly just "that one looks better/worse/opinion")