Why is Janna considered so cancerous?

Janna has some of the best peals in the game, and when you combine that with ardent censor abuse (from her shield, and an AoE constant use from her ult) it makes her extremely effective. Another big reason is most ardent censor abusers do it by healing, and healing and be stopped by grievous wounds. Currently there is no way to make a barrier smaller or cut a barriers effectiveness down so barriers are the most potent form of protection and hers is on a very short CD. So with the combination of AoE ardent heal, Huge barriers for protection that cannot be stopped, and 3 outta her 4 skills offering some form of CC she is currently the best support in he game currently in my opinion.

I should have also added that janna is 100% dependent on her ADC being capable so low Elo Janna is much less effective, but combined with a good ADC player she is pretty godly.

I find lulu worse, at least janna doesn't basically stun you for 2 seconds with no counterplay

Janna isn't cancerous, it's ancient coin that's cancerous.

q = cc w= shield e= slow r= engage/disengage