Yes, Chez Scheme is fast but it took a lot of time (a few years!) to make the compiler translate Rhombus/Racket code to fast Chez Scheme code. And there are still a few rough corners to fix...
Also, Matthew implemented flonum unboxing to make code that uses a lot of floating points like x10 faster. I added type recovery, that gives a 10% boost in many cases. And I'm probably missing a few similar features.
In most cases the Chez Scheme team also was involved. Those changes were upstreamed, so you can enjoy them in Rhombus, Racket and Chez Scheme.