They've yet to master their own 10nm process let alone 7nm. I don't doubt their processes outdo the competitors on actual die shrinkage but they've been having a hell of a time of it.
The problem with 10nm is that they were too ambitious and tried to do it without EUV. 7nm is being developed by a different team and does use EUV so it shouldn't suffer from the same delays.
From what I understand they are not really comparable like that. It’s like clock speed, there are a lot of games that can be played, and X 10nm can be much better than Y 7nm.