Infinity Edge suggestion

Why not instead of having convert 10% of your crit damage to true damage have cause your crits to ignore a percentage of the enemy's total armor (say 20%). It would be effective at helping kill tanks without feeling unfair against squishy champions. Maybe to compensate the true damage loss give it +5% critical strike chance that doubles to 10% with its passive or give it back its AD.

Do you feel this suggestion is valid? And if not why?