I'm well aware of Xeno. Since then, 2 games that were on the pipeline were cancelled, though, so the series should have been more active than it is.
I don't know about DLCs but as far as I can tell, Reborn expands the game by promoting an NPC to playable, reworks the battle system and removes the ridiculous soft porn stuff related to ending the career early, something that should never been in a game like this in the first place, so for me it's a more proper MM game than the original Xeno.
All told, I agree MM2DS and MM3DS are likely the peak. It's a shame we never got MM1DS, as I very much enjoy franchise parity.