There are three types of ships in the cinematics. The Dreadnaught, only of its size. Thousands of Tomb Ships. And a few "capital ships". We know those are tomb ships because we see them not only in perspective to the Dreadnaught, but also to Awoken trident ships and Fallen Ketchs. They're tomb ships alright. Not large ships designed to look like tomb ships. Also, I doubt Bungie would fall for such a childish mistake in making two things of different sizes look exactly the same. It makes perspectives difficult.