Well, i voice my concerns for janna in many occasions, it's just the people somehow have that wierd idea that supportive champs, especailly enchanters, can't be broken under any circumstances, and the mains of those champs are generally delusional about them(not all though). For example, back when Sona(who has only slightly worse stats than janna) had a 58% win after her mini rework, there were still some sona mains claiming she was balanced or even weak.
Now on topic: I truely belive that consistent high winrates with atleast decent pickrates are a strong indicator for an inherently to strong kit, especially if those stats are hardly impacred by noumerous number nerfs like it is the case with janna, and that those champions might need some changes to their kit.
Janna probably has been hit by more nerfs than nearly any other champ, yet her winrate hardly ever dropped below 52% at any point since her existence, cause she still hardcounters about 50% of all champs(prettymuch all melees) while offering good alround utillity on top. They nerfed most of her numbers, touched her passive and W a bit, but they never really touched the main issue that causes her to fuck over anyone that tries to enter her backline: Her Q+R. She got two buttons that just instantly cancle any dashes and stuff on aoe. If janna has well enough reactions, there is nothing that almost any melee can ever do to reach her carry, that also gets shielded and healed in the provess and gets a BFswords worth of ad ontop.
For Ahrie, i think the mix of massive mobillity, lots of damage and one of the most potent hard ccs in the game allows for insane pickpotential, just that she at the same time has a great laning phase with good early pushing+tradeing and some sustain(which about all other mages lack) with good safety from her Q speed and the ult, and at the same time strong teamfighting cause of her high mobillity(asy positioning), low CDs and the truedamage on Q that allows her to wear down frontlines quite effective for how high her kill potential vs squishys in the backline.
She does everything but waveclearing well, and even excells at geting picks, She's a jack of all trades and master of none one, and that's not ok.
If you are a good alrounder, you shouldn't be allowed to have somewthing that you excell at aswell, or if you excell at somethng, you should have some weakness aswell.