You're taking the wrong conclusion, "Fast" is a winning differentiator only when you offer the same feature-set, but faster.

Your example says it, people will go, this is like X (meaning it does/has the same features as X), but faster. And now people will flock from X to your X+faster thing.

Which tells us nothing about if people would also move to a X+more-features, or a X+nicer-ux, or a X+cheaper, etc., without them being any faster than X or even possibly slower.