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.
I think it is unfair to judge the very early D100 and D70 by current standards, digital cameras have evolved a long way since then both in technical terms and the UI. In the early days there were so few camera models that the modern lineages were yet to be established.
I've never handled a D100 and don't know what the UI is like, but it clearly is the start of the line which lead to the advanced/semi-pro D200, D300, D500 etc, so I feels it belongs in this group. The early models may seem to be mid-tier by today's standards, but the D100 and D200 were advanced cameras where they were new.
The D70 was introduced for the enthusiast, a cheaper alternative than the D100, and is clearly the start of the line which evolved into the D80, D90 and D7xxx. I remember at the time the reviewers spoke favourably of its feature set compared to the equivalent Canon model - front and rear command dials and DOF preview are not entry level features. OK, so this early model does not have a battery grip, but the replacement D80 does, and two generations later the D7000 supported AI metering.
The D50, which was introduced a little later as the entry-level model also shows that at the time, the D70 was pitched as the mid-range model.
The Df does not fit neatly anywhere, I put it in the "advanced" section partly due to the price, and the manual controls do require the user to have "advanced" knowledge on how to use it.