For me, the mish-mash of different architectural styles looks fine.
But what does read as incongruous and jarring is seeing the Grimmauld townhouses jutting right up against a theater. Universal has created what looks believably like a London high street (or in North American terms, 'main street'). As such I can fully accept that a subway station, shops, and a theater would be lined up next to one another. A row of residential houses, on the other hand, seems out of place.
So I do agree with Teebin. I think that Grimmauld would look better if it was spaced a bit further from the rest of the buildings. Even an alleyway would help.