If anything, AMD is small fish when it comes to TSMC's 7 nm production. The issue isn't capacity per se, it's more that the wafer costs are insane at 7 nm, and early on it's even worse. That's why you are likely going to only see very high margin products from AMD (and nVidia) until the middle of the year at the earliest... and that includes Ryzen.
But are 7nm prices really that high? For one thing- Apple's chip is ~83mm2, and is estimated to cost $72 to produce. Ryzen chip would be bigger, but also, Apple probably does not do much binning.
Another point of reference- AMD were estimating 2x cost to produce a 200mm2 chip on 7nm, compared to 14nm. Considering how much smaller 7nm Ryzen would be, and better yields on a smaller chip- that also suggests reasonable pricing.