@Riot, re: Champ Mastery after champion changes

I'm not entirely sure if this is the best place to put this, but I felt this was an important thing to talk about.

So Illaoi just received some buffs, so I decided to play her to see if they were effective. I've only played a handful of games, but I believe they did the trick. I got S ranks in 2 of my 5ish games, so now my Illaoi is Rank 6. Now since I was rank 5 I'd obviously played her a lot in the past, but I hadn't played her in months before those S rank games. Just to reiterate, this is not a post about Illaoi's current strength (technically).

Correct me if I'm wrong, but as I understand it champ master grades are based on player averages. A grade like A- means you performed about as well as, I dunno, top 5% or something. If that's true, if most people do really well with a champ, it's harder to get higher grades. That also means the reverse is true. Essentially what I'm saying is, though I am a somewhat experienced Illaoi player, I don't feel as though my play was especially good. I feel the S ranks I got, while well earned, were more the result of poor performance of the champion in a less viable state rather than a sign that I'd mastered Illaoi. Put yet another way, whenever a champ is changed in such a way that it significantly changes their performance, champ master will be greatly (though temporarily) affected. Until enough people play Illaoi to raise the averages, getting good grades will be "easier" (assuming I'm correct about Champ Mastery being based on average performance).

My question is are potential swings in S rank acquisition acceptable when the point of the system is to have some meaningful way to demonstrate player skill with a champion? If Taliyah were to suddenly become pick/ban after her performance in 6.10, players could get S ranks simply by functioning well in a game. The problem would be gone by the end of the month (maybe even in a week or a day), but a few mediocre players with rank 6 or 7 might compromise the meaning of champ mastery.

Since this is based heavily on information I don't know for sure, I'd really appreciate confirmation one way or another.