Rock paper scissors is inherently flawed as a metric of random outcome because it can be manipulated both by subterfuge and by pattern knowledge.
The basics is that LARP was designed around the fact that dice are a bitch to roll in the park in the middle of the night.
We don't have that problem in a MU*, dice are right there, so why not use them?
The biggest problem honestly comes from typing speed. That's not going to change based on what system you use, people will still have to type out their actions, and reactions, and on table-top we simply roll the dice, do a quick description of how we hit/got hit, and then move on. In LARP we don't take 5 to 10 minutes describing the results of our actions either.
What it comes down to is the medium we're using, so we come up with work arounds that work or don't work based largely on personal opinion.
Unless you're dealing with coded combat, like MUD level coded combat (Some MOO's also reach this level, and possibly other games I do not know about) then combat resolution is going to take a lot longer than it does in table top, or larp.
So in the end: Ruleset doesn't really matter in the long run so long as everyone understands the rules because it's waiting for people to pose that's slowing things down more than anything else.
I've experimented with a few different methods over the decades, and the one I found I liked the most (Just my opinion) was when running a scene I had everyone do their dice actions /without posing/ and then at the end of the round everyone did a pose of their action/reaction. That way people could prep their pose after their turn while waiting for the dice resolutions and it went much quicker.
Not a perfect solution, but by far the best I've discovered for our hobby.
Just my opinion.