Yeah TheMistCollector keeps updating his existing guide and thus he keeps his high rating. It's not a reflection on the quality of his guide now or in the last 2 years to be blunt. No idea if he's anywhere near Challenger right now. I don't agree with what his got there for S14 either. Terminus is a very niche item that isn't good on Senna because it takes 10 on-hits to stack and Senna's main damage combo is 3. Senna is too squishy to stay in a sustained output fight even if there was one which is why Lethality has always been her preferred build path. And yeah it looks like he's just dumping anything and everything his "Last Item Options" bucket.

Having said that, try out everything and see what works for you :) Senna does output well on an attack speed build as well but I can't even consider giving up my 300+ heals, 45 ability haste and insane burst damage. Opportunity being added (move speed is very very powerful on Senna) and Serylda's getting lethality are insane buffs to Senna.

Trinket, Umbral are already enough to justify it. If you go bork or youmuu's then that's even more reason. Feel free to change it in your own setup just try not to be an *** about it.