As a Janna player it seems like Riot is trying to bring back E max Janna but make her more interactive. These changes don't fix these problems because of multiple things.
1. When someone is diving into the backline, Janna just doesn't prep a shield on them. That doesn't work because the shield dissipates. Janna players usually stop the engage with Q, then they W or E. The play style that the changes are enforcing are kind of first shielding the target, then letting people engage on them and using Q and W to get them off, and then using E again. This will probably lower her skillcap because you don't need to stop targets with Q anymore. There's less of an incentive to start the disengage combo with Q than how it currently is.
2. These changes severely hurt W max Janna which most Janna players are happy with. W max Janna is a fun playstyle that makes her interactive. You can get poked out by walking too close for a W and people can engage on you. She isn't a shield bot with W max. Also W max mid with full ap is just a fun playstyle that Janna players like to play when support gets boring and this is kind of killing that off.