They nerfed Senna because she was "broken" and then they started buffing ADCs
Multiple ADC items have been buffed.
Runaans, Yun Tal, Berserkers (senna doesnt use)
and next patch stormrazor
If the problem was other ADCs being weak, why did they nerf Senna?
She is now weak because she has significantly lower winrate than easy to play champions like Jinx