That's the primary issue with the concept of distinguishing them. What exactly does it take to constitute an "original" work vs a submod of any one, or multiple modifications? The category for "original" is easy enough to figure out, it's the kitbashed mods made up of multiple modification's pieces and/or the ones based mostly on other pieces that are much harder to define at which point they become unique vs submod of one or more pre-existing mods. If it is more than one mod mashed up, which one is the one which gets credit as being the mod that it is a "submod" of? These types of things are hard to figure out and distinguish in a concise, clear-cut way that everyone can understand and recognize.
There was some blow-back for the concepts addition, but for the most part that went smooth enough mainly because the criteria for moving on up to the mods section was very straightforward. In this instance there are several bases to cover which is where the problem lies and will certainly ruffle feathers along the way in trying to define the different "tiers" of any specific mods. It's a tougher one to implement because of the many portions in-between really, I think most would agree a straight reskin of X mod is a sub-mod, but it's the ones that are either mixed components of other mods, or have some changes, at what point do they get separated? That's the issue I see anyway.