How to fix current AD Carry dominance
The problem is specifically critical strike and the interaction with Infinity Edge. Critical strike is too valuable of a stat, and as such it outshines all other stats.
In non-MOBA games, critical strike is only valued if you have abilities that scale from it. For example, fire mages in World of Warcraft gain bonus critical strike from all sources, as well as getting a free instant nuke by critically striking twice in a row. Because of this, they value crit over haste, but frost mages value haste more than crit because they don't have Incineration and Hot Streak.
To translate that into actual buffs and nerfs that can occur, we would need:
Critical strike damage bonus reduced from 200% to 180% Infinity Edge critical strike damage bonus reduced from 250% to 210%.
What does this do in terms of gameplay? It nerfs all crit-reliant marksmen without nerfing non-crit marksmen. Champions like Tristana, Graves, and Jinx that rush Infinity Edge would be affected, without affecting champions like Kog'maw, Lucian, and Ezreal who don't. It would also change optimal builds for these champions. Common builds would start to include items like Zephyr or Black Cleaver in place of Infinity Edge and Statikk Shiv. Essence Reaver could find a place in the game.
Now what of the champions whose kits synergize with crit? Currently the only champions in game with kits that synergize with it are Tryndamere, Gangplank, Master Yi, Yasuo, Ashe, and Garen. Though the critical strike nerf would nerf these champions, critical strike would remain for them a more valuable stat than AS or ArPen. They would still build as they do and use their crit synergy.