The problem is what is reported to the pool.
kano knows if it is an S9, because the miner tells the pool what it is, same with the A6+
He can only compare the numbers that he has access to, he can't (I think) separate out the A6 from the A721. Most likely because they are running the same software. Also the S7 (and older) does not announce itself like the S9s do.
No, the problem is that you have to do bullshit "tricks" with the numbers to in any way decide that an A7 is measurably better than an S9.
You can fanboy fudge the numbers all day and I can knock them back to reality all day...
S9s are a steaming pile of bullshit, but the cost less to run (in the long run [100+ blocks]) than A7s, and therefore have a better ROI... It's that simple!