Heh, some people's strafing in Quake is anything but simple to track. Good players don't just move left and right in consistent patterns.

UT2003/4 fights can be very taxing mechanically

ah, you beat me to it. I linked some videos that highlight strafing in quake. Here's my favorite ut2k4 vid that would highlight what you're saying

https://www.youtube.com/watch?v=uSoE44v1CTQ

holy crap, that was exciting. so much to say, but would only spoil it for others.

strafe jumping in quake is far from trivial also various weapon aided jumps are required to play at the highest level, ut also has its own dodge jump mechanics and shield jumps. https://www.youtube.com/watch?v=A1MJPMl8B5Y

the engine physics explanation is explained here https://www.youtube.com/watch?v=rTsXO6Zicls

being unable to execute this during a match like a duel means being at a massive disadvantage.

example of good strafe jumping coupled with a plasma jump to secure map/item control and pressure the opponent on the back-foot. https://youtu.be/GFTmYD95-cQ?t=1592

You should watch some quake 3 compilations, I'm sure no game today matches them. Even if they're more "complex".

>They are mechanically fairly simple.

Compared to an RTS, yes. Compared to tactical shooters like CS, no. Once you reach a certain level of aim, movement and the associated mechanics become the main distinguishing factor along with using the sounds in the game to track your opponents position and conceal yours.