Does decentralised mean slower?

It looks nice (visually), that’s for sure. A nicer Vuze client with Vuze running in the background, so to speak.
It relies on the “ordered” fetching, what Vuze has been doing for a few years now (if you pay up).

It doesn’t have to be faster since you can’t watch it “faster” than the speed it needs to playback at (I assume they don’t support unlimited fast forwarding, since for that you always need to wait).

It has to be just as fast as the playback speed is, with some buffering to survive hickups along the way. So it keeps the buffer stuffed and drops in performance are irrelevant as long as the average speed is sufficient before the buffer runs out of juice. And even before that it can switch to a lower resolution to survive a bit longer.