If the 7D2 had 61-pt AF, 8+ fps, top-of-the-line weather sealing, etc., and the entry-level FF just had image quality and ISO going for it. Even if it takes a lot of corner-cutting to offset the extra cost of the FF sensor, there are a lot of corners to cut in such a complicated device.
Just buy yourself a 1D series camera, ok?
I have no interest in something that heavy, nor can I afford the more recent entries in the 1D series. I'm not in the market for a 7D-like camera either, since I rarely shoot things that move. You asked how a 7D Mark II would sell against an entry-level full frame, and my suggestion was that it would sell just fine against an entry-level full frame with nothing going for it other than being full frame.
I kid you not, if Canon released a camera with a full frame sensor that only went up to 400 ISO, shot 1 FPS, had only one autofocus point, and no weather sealing, but had 14 stops of DR and virtually nonexistent noise at ISO 100 (or even better, native ISO 50) for under $2000, I would buy it. Today. And I bet you I'm not alone.
Everyone wants something different in a camera, so having competing models at the same price point expands the potential market at least as much as it cannibalizes sales from other models. And if they have a camera that caters to a market that the competitor doesn't have a foothold in, then the sales they're cannibalizing are someone else's.