As far as I understand it, besides the fact of stellar people working on emus like Dolphin, the hardware on the GC/SW/Wii are much simpler and closer to that of

As far as I understand it, besides the fact of stellar people working on emus like Dolphin, the hardware on the GC/SW/Wii are much simpler and closer to that of the hardware it's being emulated on. That provides for an easier translation experience when emulating each bit of hardware. This is in contrast to not as closely matching hardware on much older systems, even if they're comparatively slower. A really good example is PS2 emulation which runs pretty well today but is crazy complicated with the Emotion Engine which does not map well to our current PC architectures. Might be wrong about this but I believe SNES emulators are now approaching "perfect" emulation which is to exactly emulate the hardware down to every defect. This is what can slow things down but will give you perfect reproduction of games. A lot of modern emulators use hacks (sometimes game specific) to achieve the performance you see but can result in experiences not like the game on a native console. All that being said though, the teams working on these emulators really matters in terms of the performance they're gonna eek out of modern day computers.