[Edi]

Dom3 and CoE3 occupy different niches, so while there is overlap, I do not see CoE3 reducing things that significantly for Dom3.

Dom3 is still the number one for epic, massive, long games where things can come out of the left field to take you tterly by surprise (which can easily happen if your opponent finds the right magic sites).

CoE3 is a much faster paced blitz game with not quite as much complexity and depth, but quite enough to provide lots and lots of entertainment and (I would say) as much replay value as Dom3.

CoE3 also provides comparatively more SP value, because of the way AI is done there. There is nothing to prevent anyone from playing e.g. one turn of Dom3 (especially if you don't take it absolutely to the max with the micro etc) and then playing switching to CoE3 for the rest of the evening for a fast game or two. Especially after Dom3 games move to the 48 hour hosting interval.

They are more complementary than opposed.