what makes it to slow?
Lack of
JIT for PowerPC UAE. Also the amiga chipset emulation is very demanding, and slow systems will struggle with that.
everthing else is faster? no graphics chipset?
Pardon?
the processor is faster than classic amigas right.
It is, but emulating an amiga is a heavy task, and it's all CPU bound. Without JIT to boost the processor emulation performance 400MHz PowerMac will be just unbearably slow.