What is your intended use with the final images? What's the 7D2 and the 70-200/2.8 (100-300/2.8 ff eq) not doing for you?
I've used worse setups in the past to take pictures of my GF's kids rugby matches, a 650D with a sigma 70-200/2.8. Occasionally I would put on a 1.4x tc. The results were more than good enough for my use. One picture was even used for the league's poster.