As someone who actually owned an mk7 Golf R, for nearly 3 years; and now an owner of a Stinger GT2, i'm pretty confident I can speak on both.
Waiting to do my video review of the stinger here is my review of the R.
I've got my stinger going to be on a major car channel in the near future as well to be discussed and reviewed.
Do I miss the R, sure. It really is a tremendous car. Smaller size, great handling, and spooled up turbo pull really made it a hilarious quick nimble car. I live where the best driving canyons in the country exist, and i've driven super cars up and down them. This is where porsche, Ford, jaguar, etc bring there cars and automobile journalist to test and experience them.
The R could carve a canyon, and then could go shopping and load up with boxes like you wouldn't believe. I also enjoyed some of the anonymity it gave me, that only people who noticed were car enthusiast who I dont mind talking to. The stinger brings all sorts of people, some cool, some not.
All of that the R still had some faults. Sure the ride isn't as comfortable as the stinger (to be expected), it doesn't have a lot of power below 2500 rpm so sometimes flooring it at a dead stop to get across the street with cars coming at you could be a little hairy. The tech in my 2016 though adequate wasn't great. The fender sound system though good... not great ESPECIALLY with the absolutely worthless sub they put in it. Backseat legroom is adequate but not great, makes up with better headroom to be sure. The DSG is amazing and I wish the stinger had it (probably miss that one feature the most) but it was annoying around town and in stop and go traffic to use.
I had a magnum SRT before the R that I loved (wish I had held on to it), the stinger feels closer to that than the R. That to me is one of the most shocking things from living with the stinger. You might say it is the RWD, but to me it is the way they feel, how they handle. Comfortable cruisers with power and space... aka a ground touring car. I've taken the stinger up and down some canyons and it was honestly underwhelming. Don't get me wrong, power and grip is pretty much there; but it leans, and it dives, and handling isn't as precise as the R. It doesn't inspire the same degree of awesome confidence that the R did. (all of that is to be relatively expected)
All that being said, like many of you on these forums I got a helluva a deal with the Stinger. At 50k it is a good car, at close to 40k its pretty amazing car. I totally get why they are crossed shopped but they're actually quite different cars. Either is tremendous at what it does, it just really depends on what you are looking for.