You know what would eliminate the power spike of a random crit?
Just tweak the system so that instead of being based on percentages, critical strikes only occur from continuous attacks. As far as I can tell, the only reason crits aren't 100% predictable is because it would be easy to abuse the system by holding onto a critical attack to harass the enemy (like a free Caitlyn passive). If, critical strikes were instead somewhat more predictable, but wouldn't go off unless you were just continuously attacking, you'd still get the damage spike that AD carries rely on, but you won't just randomly chunk someone's health out of nowhere; they'd either be getting punished for being in your range too long, or it's a result of the enemy pushing the lane.
Just some food for thought.