> What are now called mosaic tiles will give a very different result because they make a square grid, more like pixel art.

Surely that’s why we call it “tile mosaics” rather than “mosaics”? Though some of the islamic tilework is really nice, it used “generically shaped” tiles but not square ones resulting in beautiful patterns (whose regularity could be broken up by playing with tile colors) e.g. zellij tilework.