Maybe it's time to rethink balance and testing
Riot doesn't often hotfix for balance issues, but 6.9 has four of them. While we all love to crack wise at the balance team, I think the problem may be more systematic.
Essentially, the PBE is underused. Not because of any failure on the part of the balance and design teams, but simply because it is too small. Balance data that can be gleaned from its limited playerbase is lacking in reliability and relevance because of the small sample size. As a result, Riot tends to discount it. But when PBE predictions turn out to be correct,it frustrates us.
I see two potential solutions. One would be a massive increase to the PBE's size, but that would come with numerous drawbacks. As an alternative, what if we drew upon the LCS?
By making normal games operate under the current patch and ranked operate under a previous one, players could have a few weeks to practice new champions, reworks, and the like without it affecting their rankings. Riot would have much more data upon which to base their decisions and it would prevent launch day ranked games with new champions.