Any such classification is going to run into inconsistencies; Nikon does not develop cameras only by improving on a single previous model but often introduces new cameras that are mixtures of features from higher and lower end cameras, thus blurring these categories.
I think the D70 belongs squarely in the entry level segment. Its user interface is quite difficult from an advanced user's perspective, it has a pentamirror viewfinder (one of the most horrible of its kind), doesn't meter with Ai lenses, has no vertical grip option and it was clearly developed with price and compactness as driving factors. The D100 also was derived from the F80 film camera body, which is a mid level consumer body. A D7200 or D750 has clearly much more in common with the high end models than the D100 or D70.
For the sake of simplicity in your listing I think the current categorization is okay. I can understand how someone might feel a D750 and D70 don't belong in the same category, however.
If I were to classify the cameras I would go with something like this:
Professional
D1, D2, D3, D4, D5
D700, D800, D810
D300, D500
Enthusiast/Advanced amateur/Semi-pro
D100, D200
D7000, D7100, D7200
D610, D750
Df
Consumer
D70, D50, D40, D60, D80, D90, D3x00, D5x00