WooHooMan
Auror
I did mention Skyrim rather than Tamriel - and for good reason. While I thoroughly enjoy the greater diversity in terms of the animals, creatures and landscapes that exists in Skyrim the urban areas and the interior of a lot of the buildings and ruins tend to be virtually identical outside of the big cities like Solitude, Markarth and Riften. That's why I am somewhat critical of its world-building. However Cyrodiil was a lot more diverse geographically, especially with the Shivering Isles, and so are the urban areas and the building interiors. Morrowind and Solstheim in the Dragonborn DLC are in a class of their own. Both are very disorientating but in a good way.
But you were talking about the Dwemer's role in Skyrim. Their role in Skyrim is no different than their role in Morrowind and Redguard. They aren't just a disappeared race meant to excuse the existence of dungeons. They are part of Tamriel's lore and the narrative of the Elder Scrolls.
Also, I'd say the buildings and ruins being similar is somewhat justified. The Dwemer ruins are distinct from the Nordic ruins as they were different cultures with their own architectural styles. Most of the Nordic ruins were constructed by the same people - the pre-Septim, post-Atmora Nords.
The towns being similar is justified by the fact that most of them are probably pretty young and were constructed by the same cultural group: Septim Empire Nords. Cyrodiil architecture is more diverse because the racial demographics of Cyrodiil is more diverse (and dynamic due to cultural exchange with neighboring countries). Not only are Imperial a less overwhelming majority than Skyrim Nords but they are a more diverse culture due to historic split between Colovian/Western Imperial and Nibenese/Eastern Imperial. But then we get into the topic of how much of Tamriel's lore is represented in the actual games which is a big and controversial topic among fans.