The problem with American Genesises and this ROM is that this was coded with a crap ton of waitTick commands, and is terribly unoptimised. Running on my PAL Mega Drive 1 with TMSS there's barely any. The video is taken on Genesis Plus GX in PAL50 and also works fine on BlastEm too. I also went into NTSC mode about 50% into completion and was like "damn, that's messed up". I will probably create an NTSC version soon.
Also, if you tested it on real hardware, what flashcart did you use? I tested mine with an Everdrive X3, by the way. I unfortunately only have a stock PAL MD 1, no other models, no Mega CD, no 32x, no video mods, no capture card.