I would just like to address a few point here. Malgus is NOT more powerful them Malgus and if you think so somethings majorly screwed up with you. Secondly the quote you gave where it says Tenebrous had grown weak and sluggish isn't that comparable to how Malgus was injured at that moment? Along with that he was not only holding up the ceiling to keep it from crushing him but also holding up the slabs that were about to crush the ship. Also blasting your way out from that much rubble isn't as impressive as holding it up. Finally faced in the same position Malgus would succumb as he would be holding up the slabs to prevent the ship from being crushed holding up the slabs to keep himself beign crushed and have to face off Plagueis's TK assault to.
All that's just assumption though as I don't believe Malgus would even be able to accomplish the feat of holding up so much stone. If he COULD however then the outcome would be the same. Along with that Tenebrous has faced far faster opponents then Malgus and I believe would also take it in the strength and endurance and skill department. Problem is so little was written about him that feats like surprising Plagueis with his speed have to be transferred based on Plagueis's own feats. It can be assumed since Plagueis was not willing to face his master in a duel that Tenebrous outmatched Plagueis in speed strength endurance and even the force given the situation. Due to all these factors I say Tenebrous 10/10.