Their demo car uses Pilot Sport Cup 2 tires, which are also used on the Buggati Chiron and Koenigsegg Agera RS (which recently set two records for fastest 0-400kph-0 and fastest production car road speed). These tires are street legal.

The Roadster is significantly faster than other supercars from 0-60 on the same tires, so the advantage must come from much more efficient anti-wheel slipping from the three electric motors coupled to AWD. This dramatic speed advantage is probably a result of the ability to quickly alter the power output per wheel to minimize efficiency losses from breaking traction.

Braking has a very different load distribution, even with a center of mass as low as in supercars. I would not put to much into that comparison. Tires are depicted as Michelin in the announcement, it would be very surprising if they keep their best exclusive to Tesla, considering the relative proximity between Bugatti and Michelin, the relative cheapness of the Tesla and Volkswagen group representing a much bigger part of the tires market than Tesla for the foreseeable future.

> it only costs a fraction of a second

In other words: exactly the scale of the differences we are talking about. In addition to the short interruption itself I guess that it also takes a few millis until traction control has settled after a shift.