this happens because there is an AW loader for Naomi in these roms that act as some sort of broker that copies data from the dimm instead of the original cart location, that code is however poorly optimized from what I have seen and uses PIO for transfers instead of DMA, which is the cause of the slowdowns. You would have to rewrite the AW loader properly so it uses DMA.@Dreygor short answer: there is no sense
these conversions suffers from significant slowdowns here and there, afaik that's the only problem. it is unknown why this happen and I have no ideas why.
ofc, you may poke Darksoft, he in it's turn as usual will poke me, and it will ends with nothing (read above - no ideas about the cause of problem = unknown what should be fixed)