question that shouldnt need any biased answers or hate

why are autoattackers do more "assassin" type damage late game and can sustain/take damage like a tank (if theres no cc vs them). why is the RIGHT CLICK so powerful? why is it more valued than skillshots that actually requires aim to use instead of instant death 1 right click assassin burst? say theres the hardest mage in the game thats created (completely exaggerating of course) where they have 5 different skillsets the ult allows transformation and each skill has its own cooldown plus they interact with each other in some way like a bonus if you used this and that specifically those types of skills . (lets just say it happened) vs well a fully itemized adc with all anti ap/one hp item (cleaver) for survival. why does the adcs 1 auto do more burst than said mage with 5 skillsets and cant run out of mana doing autos. how is that a fair concept? if your more skilled you should be able to duel a adc by skill and for some reason all the adc has to do is right click once.

short version is: why does adc do more assassin damage then other classes plus why doesnt it use mana to crit as a limiter. i mean if a adc has 100% crit that have to give up something for 2x damage right? so why not mana for crits.