DCU at 7.99 and MU at 9.99 isn’t much of a difference except MU has a much shorter wait time for books (6 months vs 1 year like you mentioned). Comixology Unlimited best asset is the variety of publishers they offer and you can find a full run every once in a while (Rachel Rising, Strangers in Paradise, Ex Machina) but yes, they typically won’t have full runs of Marvel/DC for obvious reasons.
The main selling point of this service to me was when they stopped the whole “rotating collection of comics” and went the MU route with it. So if they bolstered that department, I’d be super happy considering I don’t really partake in a lot of the media unless I feel nostalgic.
Comparing MU and DCU annual memberships of $69 and $74.99, respectively, going the comics only route works for me.