Okay now that I've baited every single ADC main in one single go into clicking here, I'd like to say that as a 22/3 Rengar, an Ashe with her only armor Item being Thorn mail managed to tank a full lethality black cleaver Rengar rotation TWICE without going under half health, while pumping over 600 damage an Auto attack into me every second.
Yea, ADCS are weak and AD assassins are broken though!
there is more to it then what youre leading on. its hard to see until you slow it down, but teemo blinded you. ergo, your combo wasnt tanked, it never hit its target:
................. the IQ behind this post is.......... there are no words for it. They are complaining they do NO DAMAGE, you are complaining about not being able to oneshot an ashe with thornmail. Maybe you forgot to say that she was ulted and shielded no stop by lulu or janna idk, or your rotation lasts for 20 seconds 'couse you can't do it well or got kited.
Wait, an adc player finally building smartly? That is something that happens every 200 games.
Yeah there is no way the scenario OP mentioned happened unless there are quite a few details he/she left out. He probably got 
'd.
there are 100% other factors, if you cant kill ashe as rengo thats on you
