This is indeed close to the crux of the issue, and you say this as if it it a trivial thing to do or an afterthought. Or even desirable.
Well I've only just started doing it, but so far turning short rest powers into long rest powers x3 seems very easy & beneficial. I don't see any benefit in having different classes on different rest cycles. When
everyone is Long Rest, the PCs find a natural cadence to adventuring suited to threat level,
urgency etc. Maybe everyone being Short Rest would be better, but much harder to accomplish.