yes, flash is faster. once flash enters the speed force it takes runner with the gem to match him. mak beat runner in a race, but runner didn't have the gem, and in that race it can be interpretted that mak only reached light speed -- he says it himself -- he became light, the essence of speed.
even if he was ftl, it's still no match for flash in the speedforce. quasar was able to get ahead of the runners by entering the quantum zone. i see no reason flash couldn't do the same.
and anything thena can do, gl should be able to match. as i said, i think sersi is tougher. you could put gl v sersi -- which would be a GREAT battle (most say gl=ss, and most also say ss>sersi, but i think it's REALLY close) but thena is likely still more powerful than j'onn.
IF you think gl can beat sersi (a possibility for sure) then the jla could win this fight.
it's really is very close.