If you had a combat system that resolved actions by the half-second, the fighter can do that without needing a marking mechanic. However, that adds a host of other challenges and makes combats really weird.
GURPS functions "perfectly well" with 1-second combat rounds. It doesn't seem to give weird results, either, when compared to many other games.
I personally don't like a character having mechanics to defend. I would instead like the general rules to low anyone to defend.
Get rid of marking, defender auras, and shifting, then when the enemy is next to you it can't get away without getting an AoO and anyone who wants to can defend.
So, encourage highly static fights and make sure that people aren't distracted in any way by being attacked while trying to do something. Not that I disagree with the idea of anyone being able to defend, but what that means is at least as important.