I’ve run a bunch of GURPS over the years; GURPS has a strong player culture, and its driven the game to change from “Model the character in your head” to “penny-pinch points for the most efficient version of the character you conceived of” The attribute scale was orignally 10 normed, long right tail… but most templates now are significantly above average.
Further, it’s gritty simulationism is a lot of hassle, especially for supers. Oh, and in Supers, a 500 point wizard dusts most 500 point supers. Mix-n-match isn’t a balanced thing,
Moreover, SJG’s playtest windows are, by most standards, insanely short.
Unlike Champions, GURPS is buy the cause. (Champions is buy the effect, describe the cause as desired.)