We talked about this a bit in the dreamteck discord when the categories were being created. I think the reason for keeping them separate is that NG+ Deathless locks your plane selection, where NG+ allows you to take tactical deaths to swap to more optimized planes (for example, speedbird is ridiculously good in the early levels, but can be overtaken by long boi in later levels).

Regarding split names, I think that's probably a good idea, just to keep things consistent