Part of the appeal  systems like GURPS  or Hero  had for me when I was into rules heavy RPGs  was the sense that they could "model reality" (their version of it) independently of the notions of everyone at the table. It was less of a sense of not trusting the GM and more of an interest of what  the system would spit out in any given situation .  Sometimes I would play test stuff on my own just for fun (did  a bit of style vs style  with the martial arts supplement).

When  I was younger I also had a preoccupation  with fidelity to reality, and it would paralyze me to have to make a ruling on something I had no idea of like the range a gun could shoot (something that's never missing in RPGs), but even stuff like how quicksand works. Now I see that as having had the wrong  mindset, but who am I to judge people who might feel that stuff is important .  

If I'd had the Internet advice that's  abundant now, I probably wouldn't have let that stuff get in the way of fun. Ces't la vie.

I like Hero System because it has a solid core set of rules and the additional abilities are managed with a coherent system. That allows me to improvise freely but with some structure. Looser system make me feel like I'm swinging in the wind with no guidance or guidelines. I prefer to have the rules there if I need them and I can ignore them if I choose than not have anything there when I need or want something solid. Plus I just like the way Hero does things and its flexibility, the system clicks for me so when I run it, it feels smooth and invisible in a way others don't.