He beat Vader by a hair, the difference between them was that Galen still had his full potential to realise, Sidious believed he could become his equal and more, not that he was his equal, but Sidious gave up on that when he died.
Galen Marek wins he could beat Revan and Vader at the same time.
Vader choked people and only rarely killed them.
revan had lightning but mostly it stunned or disoriented people and did moderate damage.
Galem would hold people and throw his lightsaber through them.
vader could lift and throw broken pillars.
Revan could pick up and trow boulders.
Galen Could rip tie fighters out of the air and throw them at people.
Canon statement Galen Marek was the only person Sideous believed could truly be his equal.
if vader was 80% of siedous and galen was equal to sideous do the math.
Galen Marek is the I win card