This is about user perception of performance: startup time, UI responsiveness, etc. Not raw CPU speed. It did fine on all those counts, even if you'd never let VB do your DSP work for you.
Granted, the platform surrounding VB6 arguably had too much hairy logic related to COM and ActiveX, and the fragile system that existed for registering such components before Windows XP introduced side-by-side assemblies. If you really want to pine for the old days, consider Delphi, where you could compile everything into one executable; just map that hunk of code into memory and go.
