Too many unknowns about Momin, unfortunately. As much as I love Lord Momin, Quinlan Vos just has more reliable showings. Vos being superior to Ventress, trouncing Grievous, and going toe-to-toe with Dooku just puts him solidly above Momin's one showing of out-fencing a heavily handicapped Vader whose servomotors were grinding from all the damage his suit had suffered.
Momin had an extremely deep understanding/comprehension of the dark side, which was beyond every other being in canon(with the possible exception of Palpatine himself, but even that's iffy, imo.) He was able to use this knowledge to construct Sith-tech like we've never seen in the mythos... That is where he shined.
In terms of his actual power/skill, however, Momin's only known feats are beating his former Master, Darth Shaa(whose powerset is entirely unknown), and besting a markedly weakened Vader... And that is certainly not enough to put him above Vos in a combat scenario.