Are we talking about the same computers?
You are probably mistaking more complex (amiga) with more tricky (c64).
The programming model on the amiga is more complex simply because you have to cope with several components (blitter, copper and the other coprocessors) whereas on the c64 you only program for the 6510 (the only coprocessor being the sid).
Asm for the 6510 is way easier to learn and use than for the MC680x0: wanna compare the addressing modes on both?
I remember programming on the c64 like comfortable but hairy, whereas on the amiga I appreciate the elegance but respect the complexity.