I agree with the systems you mention. Hackmaster, as I understand it, is pretty complicated. I had a game called Nephilim, and that seemed pretty complicated to me, but I think it was a derivative of the BRP system or something.
I tend to lean towards simpler systems, though.
Hackmaster 3rd and Web of Stars dust Hero, GURPS, and Rolemaster on complexity. Rolemaster front loads, as does Hero; once characters are generated (and in RM's case, the weapons charts copied), it's very simple in play. SpaceMaster is slightly more complicated, because of adding ship rules. Alternity is about equally complex, as is AD&D 1E with all the expansions.
GURPS complexity is mostly in character generation, but also in rules selection for the various optional graft ins.
Space Opera is more complex than GURPS, Hero, or RM, because many of the some 150 skills have unique formulae and modifiers. Run "from the book" it's not horrible, but you NEED the book to run it as written.
Hero, GURPS, Rolemaster are all simple cores with a zillion options. Hackmaster 4 is actually a straightforward core with many options. Same for Burning Wheel and Burning Empires.
Phoenix Command (and its related games) is heavily formulaic, but the tables make it playable with a 4-function calculator. Cumbersome, but playable. The Aliens Adventure Game is the "light" version, and I'd put it on par with Hero, GURPS, and Rolemaster.
Web is not a simple core. It's heavily formulaic. I have had issues even following the character gen. The expansions are terse and formula-filled. I've only got the Web of Stars. Across the board, it's more complex than Hero, GURPS, and Rolemaster.
Hackmaster 3rd is also not a simple core. It's intentionally cumbersome.
FATAL is insanely complex, but that complexity is in places that sane players won't generally use. The core itself is not overly complex. The rules for effects of rape are complex and brutal. It's a disgusting piece of work, glorifying sexual violence....