Computers and GPUs are stupid. But manipulating the osm data isn’t a way either. The walls and roofs may in really invisible merged. Or there is a gap, a line of isolation. Anyway, yes, it would be nice to see the single houses. You only may ask the renderer to add something in the code.
It really would be help, if you mention the OSM-ID, so I could investigate.
OSM is ready, but each renderer has to handle it. Yo you know were to ask 
I am not a fan of commas, it mostly is not exact. I prefer the degree value. Do you really expect the rendere to allign to the way rectangle 
double_gabled is odd. I see multiple building parts. Otherwise you need to tag the building heights as an;value;list. May be no renderer will ever support that.