Normally you’d be right. But Nintendo is just kinda bad at a lot of technology. Pokemon cheating, preventing hacks on their HW, bug bounty program, etc. To say nothing of their issues with older games being emulated etc.

From their track record id expect them to outsource to a vendor for the voice model. Then there is some minor problem that gets fans mad. The vendor fixes the problem but Nintendo decides that all attempts in the space are doomed and doesn’t touch ai voice for years and uses a stupidly over complicated solution in the interim.