This is definitely a feature of GURPS. Everything is built to be customized. I often hear people refer to GURPS as an RPG Toolkit rather than a single RPG. (Though it does have a number of fully fleshed out genres like dungeon fantasy, action, post-apocalyptic, etc.) Despite playing GURPS for decades now, I haven't invested much time into the customizations. The primary draw of GURPS to me is the way the mechanics support building characters of all sorts. I like the way disadvantages and quirks can round out a character for role-playing purposes.
I know there are lots of people who customize the magic system, though. I've played in campaigns where there were multiple magic systems in parallel, each extremely different from the others. Cool stuff.
This is a fair hesitation, but it need not be an obstacle. The default combat system in DFRPG is simpler than full GURPS (especially with all the optional expansions from Martial Arts and similar books), but it can be simplified. I played GURPS for years in the '90s without using hit locations, for example. This reduced the number of tactical choices and brought it closer to D&D's hit point attrition model, but it also sped things up for a group of mostly new players. I've also often run it "theater of the mind" without using a combat map. (Though with VTTs during COVID, I've become fonder of using a battlemap.)
My players and I have been experimenting with ways of adjusting the granularity of combat to suit the scene. Dropping into "bullet time" for moments of high tactical drama and then zooming out to simpler combat when battling hordes of mooks and whatnot. It's an easy system to tinker with.
