Thoughts?
Janna is seeing some pretty regular nerfs and has been since pretty much forever. It's not like Riot hasn't touched her with the nerf-bat.
Also: I feel a bigger issue with Janna is more about what supports are allowed to do in LoL and how support kits are set up in general.
Generally speaking, having good bases that stay relevant through out the game is the most important thing: as due to solo-lane balance, good scaling and low bases just means being weak the entire game when playing a champion as a support.
For whatever reason everyone has AD or AP ratios on everything and in pretty much every case those are proportional to the base damage a skill offers, which mostly makes kit-power devoid of AD/AP scaling (most CC, knockbacks, MS boosts) the only real option in regards to picking a support champion that will remain relevant throughout a game, and Janna is simply the embodiment of tons of utility and no-damage to begin with, making her a natural choice.
In several regards Janna feels like a better support than most more for reasons like a champion with a good kit being bad because they lack decent itemization. She isn't game-breaking so much as hardly any champion in LoL is actually optimized to be a support. This is especially true since Riot added carry-scaling on the utility of several supports, exacerbating the problem of support's capacity to abuse solo lanes and thus being nerffed to the point they're only a support because they can't do anything else and they're really weak at the roll, and champions like Janna that don't have a lot of utility to cram ratios on are naturally going to be better because she doesn't have a lot of nonsensical ratios. When you have the option of running a carry, carry, utility carry, carry, or Janna as a support: the choice is pretty obvious.