Look at the N3DS version, versus the Wii U. What further corners could they have cut, for the OG 3DS version to run better? It'd have been that shitty without the N3DS even existing. It was beyond the system, full stop.
Really they should have made a game from the base up designed for 3DS hardware, no porting at all, the system wasnt meant for that game. But this is just like how I hope devs make games designed from the base up to run well on PS4(and/or Xbox One for that matter) hardware rather then designing a game for PS4K hardware and gimping it down for PS4. The former results in a better experience for an OG PS4 owner.