These casting changes are part of what are going to be some completely game-altering decisions and they are just extremely ill-judged.
Summoner is strong, but the writing on the wall seems to be that it's going to be nerfed, and that's because the players on the lower end of the experience tier haven't yet learned how to handle them yet. In time they would have. Not anymore.
And at the same time, the devs are adding an interruption threshhold which will make already smart/good blms and whms ridiculously overpowered. The devs are basically giving them license to freecast anything they want. It's why I say ill-judged because the game is going to gravitate towards whms and blms being so far at the top of the food chain it'll make a current smn look like he or she is completely useless and they'll be marginalized out of the mode. You're going from one job being strong to two jobs being grossly overpowered. How does this solve anything?
Part of the problem is that it seems the devs are just looking at aggregate data as well as people complaining on the OF. Obviously you want to listen to your constituents and look at your data, but it doesn't seem as anything is going on beyond cursory review. It sure just seems like SE is looking at a piece of paper and arbitrarily going "oh yeah i guess those posters are right, according to our records SMN does do a lot of damage, so it must be as overpowered as they say, right?" But that doesn't actually look into the complete depth of what's going on, and now it seems as if a balance change is coming based on arbitrary judgments. To really know what's going on you have to play myriad hours at peak levels, but instead changes are happening because of anything but. This is very, very bad for balance.
If the intent is to create better pvp balance, that's fine. That should absolutely be a priority. But execution matters, and if you just follow through on what the mass of inexperienced players want without actual taking true competitiveness and in-depth analysis into account, balance can't be achieved. And what's likely going to happen now is just a dramatic shift from what actually was ok for competitive balance into a scene where blm and whm are going to completely take over.