I'm revisiting a previous concept of mine. Back to the concept of a residence in the Human world that is essentially an attempt to recreate a little patch of Equus in that realm or is at least an attempt to anchor the two worlds together.

some more ideas:

The reasons as to why the architecture of some of these residence would not jive with the contemporary American architecture of Canterlot City would be because they didn't come from that city and also not built in the modern dau. Like they were imported there. Originally built someplace else in an earlier time period in Human History and then moved to a new location. Whether that be some place in the Human world or some place in Equus.

There could be this thing where through some unfortunate circumstances, the house or mansion was disassembled but was never reassembled at the new location. leaving it in unassembled pieces:

some of these pieces would end up in other buildings in Canterlot City, causing them to take on the magical properties of the repurposed stones.

To keep with the "Wizard tower" trope the design of these mansions all consistently have a single large tower where the owner's study and living quarters are located.

The architectural and artistic style of these structures would reflect on the personalities these magic users had in Equus as well as the magic they study and wield.

Like an example and an idea is an Art Nouveau Mansion denoting a wielder and studier of plant magic who in the pony world, was of the Deer race in Equus.

This architectural style is chosen as an attempt to recreate his former home of Thicket in Equus. Having this sort of organic style that emulates plants such as tree, vines and flowers and has emphasis for large glass windows and skylights in a clear attempt to emulate an ornate greenhouse.

The residence would seemingly be designed to function as a greenhouse to nurture the various Equestrian plant specimens in the Manor.