The biggest issue was developers didn't make N64 games follow any standards. Many used shortcuts, and even holes in the system to get the games do things they weren't normally intended to do. So it makes it highly dififcult to emulate for every game the same way.
Yep, old consoles where devs wrote against bare metal or at least with developer/publisher specific codebases that did whatever worked to get speed. Inaccurate emulation requires a ton of game-specific hacks and accurate emulation requires more power than the mini has to offer.Perhaps one day we'll see an emulator that strikes a good middle ground, for now at least the price of a conker cart pushed me to get a 64drive instead years ago.