Sorry I must take exception to that.
They both had 68000 processors, and the Amiga WAS faster due to the PAD chip set which meant the processor had more time for boring shit while the Paula, Angus and Denise chips worked on the graphics and sound.
The reason Atari games were faster at first were, as I mentioned earlier :
a) they were straight ports from the Atari with no code dedicated to the extra hardware the Amiga had
b) programmer's did not understand how powerful the blitter was, which is what happens when new technology is available.