Six onion-roof towers supporting heavens

[Koen G]

Personally I think they are vessels, some would make pretty impossible buildings. The one on the right for example - in the central group. 
Interestingly though, the drawer seems to recycle some aspects between buildings in the ROS and pharma vessels, whatever that might mean.

I think so too. Even just looking at the pharma vessels in isolation, it's not hard to see many of them them as little towers on pedestals. But I agree that it's hard to see any of the six items on the rosettes as unambiguous towers, even though this appears to be people's standard interpretation.