Say that lorgar can beat abbadon in a fistfight.
So what?
I repeat: SO WHAT?
Being the warmaster isn't about winning a fisfight with one person. It's about strategies, logistics, long term planning, organization, etc.
Even chaos filth knows this.
Maybe a
CSM warband or an ork mob can be ran based on who wins a fistfight, but armies don't work that way very well. I'm sure a lot of privates in the army could have wiped the floor with Patton. Rommel was known to be a somewhat small man physically. It didn't matter. They were better leaders.
Abbadon despite the jokes about his ineptness for 10,000 years of fails (Which turned out to be a long term plan worthy of Tzeentch himself) is simply a better long term planner, strategist and leader than any of his rivals.