I have (amongst others) both a D7100 and DF
IMO they can't be compared
First and foremost there simply is a huge difference in IQ, that of a top FX (D4, even if the D5 sensor is even newer/better) sensor, and a already somewhat outdated (by the D7200 and D500) DX sensor.
Also, the full frame DF a much better high ISO (easily up to ISO 12800) then the D7100 ('only' IS0 3200 at best) .
That said, IMO the D7100 has a better IQ then, although a similarly 'limited' high ISO to the D300 (have owned one), while on the other hand the AF and buffer (and built quality) of the D300 are better.
The D7100 still can do a decent job nevertheless, although I agree with the observation that getting a sharp image is just as, if even not more, dependent on proper shooting shooting technique (simple holding the camera in a balanced way) and correct AF settings (automated everything AF may seem convenient, but will always be a compromise as it may not focus on what you wanted it to focus on)
And of course don't forget that its higher MP is less forgiving on low quality lenses then the D300, e.g. my kit DX 18-55mm zoom which was my 'go to' lens on my D300 really wasn't up to it on the D7100 (had a similar experience with some of my FX lenses when I went from a D3 to a D800)
Used the D7100 successfully for shooting catwalk (which considering the subject matter - fast moving subject under often not ideal light - is quite challenging) though, so stills etc really should not be a problem.
In my experience it compared to FX just needs a bit more work in post to get the IQ up to an acceptable level (and I'm not a pixel peeper)
Between the DF and D7100, I find the AF quite on par, just like the built quality, while the DF has a better buffer (although, if you select 12 bit fixed compressed RAW without Jpg, you can up the D7100 buffer from 5 shots to around 10 shots)
That said, the price (both MSRP and 2nd hand) of the DF is a bit, arguably much too high, considering Nikon has alternatives with basically a, apart from IQ and high ISO, in many respects quite similar (D610) and even superior (D750) performance, which have a for 'daily' use much more conventional /better UI (having in the past shot bodies like a F2 and FE for a long time, I personally don't mind the DF 'knob and dial' set up)
I personally bought a DF as I wanted a smaller, lighter, digital body that was better balanced with my old manual Ai lenses (which even on a D800 feel too small, let alone on a D3 or gripped D800) and for me it really is the best Nikon DSLR for use with manual lenses, e.g. also used it with Petzval lens
http://m3.i.pbase.com/g9/20/670620/3/156857543.BpZnCiEN.jpg(DF 2.2/85mm Petzval ISO 100 f2.2 1/360th)
Got the D7100 (2nd hand) as an upgrade for my D70S (great little camera, but UI and IQ were starting to really feel outdated when used next to my FX bodies) and D2X (basically broken due to a bent lens mount, repair of which was considering its age, and high ISO, for me not economically feasible)
But for me it's just my 'tag along' camera, for the occasions I want to be able to shoot a better picture then with my phone, but don't want to take my more expensive (and bigger/heavier) FX bodies with me