When I got Buka, we already had a fairly dominant dog, Sally. Sally rode Buka like no one's business the first couple weeks. I worried alot for her, and tried to protect her, but in the end, it was just dogs being dogs, and the two of them made their own relationship.
Fast forward 10 years: When we got Amber (our sick shelter dog), Buka followed the teachings of the wise one, Sally, and was all over Amber's case for the first few weeks. We would joke that she was taking Amber to school. I didn't worry this time, because I'd seen it all before.
The long and the short of it is, dogs NEED a hierarchy to function with one another, and they have no qualms about playing the domination game, even with little puppies, when they first enter the pack. The thing is, when you watch closely, you can see that in the process of playing Drill Sergeant to the little spud, the bigger dog is not just dominating, but also teaching. They teach the little one how to deal with aggression, where their place is, who gets to eat first, and all the other things that keep dog packs humming along.
So, don't wory about Ace and Eca. They're just making friends the way dogs do. It looks bad, but it works for them. Amber and Buka are real buddies now.