I disagree - everytime they've fought Luke, Ben and now Dyon (who isn't even a Jedi) they've suffered heavy losses. That stupid High Lord Gaalan wasn't even close to defeated Luke in a lightsaber contest. If he didn't hop on the shuttle, he would have been KIA like the other two Saber's. Rememer, there was more than three Sith and it is possible they were aiding him to lift the shuttle.
These Sith are not chumps, but no where near the level of power that Revan, Bane, Vader much less Sidious wielded. And Jedi fought all 4 of those Sith. It is possible that they (Tribe) did not know of the Force abilities like Force Storm. We have to take into account that these are not Old Republic Jedi, but post - YV and Second Galactic Civil War ones.