I also think Zeromus was amazingly hard, even in the US SNES version (FF"2"), but that was because I was playing on the fastest battle speed, which makes things a lot harder. With the fastest speed, Zeromus was hard until you get to levels 58-60+ in the US SNES version, at least for me. With the fastest speed in the SNES hard type version, he was almost impossible unless you reach levels 60-65, and even then he was really hard. In GBA, I've only fought him with the normal battle speed around level 65, and I found him really easy.