Nihilus was utterly destroying her. She only survived due to her Force wound and Visas Marr weakening Darth Nihilus by severing their bond. It's not a feat.
And besting Darth Sion, a powerful Sith with absolutely no combat abilities to boot, is not more impressive than besting Bastila Shan, the most prodigious Jedi of the Order with actual feats to show.
And putting Malak, who has the power of the Star Forge and numerous Jedi to draw upon, on his ass three to nine times is definitely more impressive than besting Kreia, who is just a decent combatant (and now without an arm) with her trademark ability not applicable against the Exile (i.e. Force drain). A simple comparison in willpower between Kreia and Malak will make clear Malak is vastly more powerful. And that shouldn't be a surprise, since Avellone wrote Kotor II with the intention of KotOR Revan being capable of besting both Kreia and the Exile at the same time. But sure, let's ignore that.
Revan took on "hundreds" on Korriban following killing the two headmasters and two terentatek with only the aid of Juhani and Onasi. This vastly outstrips the Malachor feat. And then assuming that him, Ordo, and another companion fought even more Sith on the Star Forge (every Sith on the station), and then Revan soloing Shan (as mentioned prior), the Infinite Army, and then Malak (also mentioned prior), he's ridiculously better than the Exile in everything.
And then if we fast forward only a couple years, Revan is capable of one-shotting Surik. Do the math.