Perhaps in the original Armbian uses its own logic of designation of the cores and the system being built I do not pretend to be true, but I try to stick to the logic of the Linux systems and "adult" distributions. In them, "default" means stable, proven, reliable in use, recommended for the average user. "DEV" is a future system that is being developed , can be improved, but can potentially contain bugs and is recommended for advanced users. "Next" is the analogy of the symbol of the Linux kernel, i.e. the image of the "next" Armbian uses the core of the "NEXT" Linux. So less confusion when comparing the user designations of the image and the kernel, which it has.
PS I do not impose anything on anyone, it is only my personal opinion.