That's an interesting thought. But since I'm sticking with the Twin souls are not conjoined twin souls...There isn't much told about any of the elven pantheon, other than Mythal who we see revealed in the game. I would have loved to either ask her or Abelas questions about ancient arlathan but since that would probably indicate spoilers the writers didn't give us that chance.
Anyways. I'm thinking that DIrthamen was very powerful, but in a different way. That he chose to remain quiet and work in the shadows. It gives him more of an advantage to do what he wants without having to alert anyone about what he is up to. So it could be that he has alot of power, but he chooses not to display it for his own benefit. So maybe I'm arguing that he put up this illusion that he was a weaker member so that no one would suspect him.
Assuming Falon'din and Dirthamen were separate entities, I picture them as being very close allies, with Falon'din handling matters in a more upfront matter, with Dirthamen acting as spymaster. Both being powerful in direct confrontation, but Dirthamen preferring to avoid conflict just by collecting secrets, avoiding wasting power. *shrug* I can also picture
June and Ghilan'nain are the ones I'd peg as being the least directly powerful. June because the stereotype of the smith god seems to be somewhat removed from the others' power politics and focused on creating the fun magical gizmos that give the heroes and gods a fighting edge, and Ghilan'nain because she seems to have Andruil as a superior, whereas most of the gods may have had only the parents of the Pantheon. (Though Fen'harel may have had Mythal, going off some interesting theories.) But Bioware could do something that would surprise me with their characterization. A craft-god that kills dragons with his bare hands to collect materials for his new enchanted cloak, a scientist that breeds horrors and unleashes them on the People to test them and stands ready to overthrow Andruil. That kind of thing.
Elgar'nan, Mythal, Andruil, and Falon'din are the ones I suspect of being most powerful directly. Assuming Liz's interpretation of Tyrdda Bright-Axe is on the mark, Dirthamen is defeated by a human mage with some aid from Mythal in the Fade. He could have been holding back, or Tyrdda could have been a Dark Souls protagonist candidate.