The benefit of FPGAs is you can get nearly gate perfect emulation of an old games system. We've had emulators for years that get most things right but some games and minor things in old games require specific software patches to ensure the odd why they used the chips available produces the same output. There's a great old article from 2011 about the power required at the time to get a nearly perfect emulation of a NES. [0] The goal with the Pocket and all of Analogue's consoles isn't to be just another emulation machine but to run as close as possible to the original at a hardware level. That's their whole niche, hardware level 'emulation' of old consoles.

[0] https://arstechnica.com/gaming/2011/08/accuracy-takes-power-...