Actually, I'd say it really comes down to rails and tires. Streetcars can be given the same rights-of-way as buses and would perform similarly, except: the streetcar is a smoother ride. I can grab breakfast and eat it on a streetcar knowing there's only one direction of motion to worry about. On a bus, however, you can never tell which way you'll be jerked around. It really is much less pleasant, even if it's faster without the right of way. (Due to left turning cars)

A lot of tram systems don't have dedicated rights-of-way.

Several cities in UK are bringing trams back.

They call them 'the metro' usually to sound more modern.

I use one twice a week, but it only runs on actual roads for a small part of the journey (Birmingham to Wolverhampton) so it is more of a light railway really. The extension at the Birmingham end will bring the trams back onto main city streets.

The incidence of that mistake seems to be increasing. It's the new "could care less".