I figured that out eventually and while it makes sense is also very inconvenient as nearly no asset packs for RPG Maker include all of those folders at the same time. The only ones I can name off hand that actually do are the 3 Japanese Asset sets, all others only provide one of those 3 sub, sub folders. It wasn't mentioned in documentation so I was super confused for a while. The error for that specifically also looks identical to not having SV and such so it wasn't very insightful in troubleshooting.
Also whenever importing MV into MZ it breaks the generator so badly I need to reinstall everything from scratch. I know MV stuff isn't exactly the same with poses but you'd think the normal overworld sprites wouldn't break as well but they do, and unlike posts about doing it, this tool breaks all assets completely if you do it with the base generator for MV to a much more destructive degree.