In a technical sense, both apps are displaying all the same kinds of things: satellite tiles, scalable road vectors, rotated outlined text for street names, 3D buildings if you like, etc. But Google Maps is dog-slow compared to Apple Maps at doing it.

Is efficient painting logic for a maps app on mobile a genuinely-hard problem that Apple Maps is being really clever at solving? Or is it an easy problem that Google Maps is being really stupid at solving?

If it's open in the background it's nearly instant to switch to it, unlike some other apps.