The 6502 was faster at accessing memory. I remeber Elite running a lot better on a 2MHz BBC Micro than on any 3.58MHz Z80 based micro, like the MSXs.

The MSX 1 also had a hideous design flaw (for a gaming machine) that hid the framebuffer from the processor. IIRC, you had to do a couple IOs to get a single byte to or from the VRAM.

I remember the MSX2 had exactly the same flaw, it had a bigger video memory and some 2D acceleration primitives, but the access method was the same, through vpoke/vpeek.