User blog comment:Krankenheimer/Critical Strikes/@comment-16737371-20140416201947/@comment-1330314-20140417182158

This is true, assuming you follow Krankenheimer's suggestion where critical strike directly multiplies your AD and thus factors into spells. That's not what crit does. Unless you're casting or, crit will not interact at all with your spell-based damage. You seem to be of the same opinion if crit simply multiplied autoattack-based damage, which is where math goes against you:

Suppose you're a champion like who gains 25% bonus AD. Now suppose you go for a ridiculous build and take a  plus four fully stacked. Now suppose you want to decide between a fifth BT or an. If you take IE, assuming the conversion is 1-to-1 your autoattacks will deal 37.5% bonus damage. Your base AS at level 18 is 1.03, which means you'll deal about 284 bonus physical damage per second. Because this is the maximum amount of AD you can have (give or take a few runes/masteries), this benefits IE the most, as it's a multiplier to your AD on basic attacks (and basic attacks only, in this case).

Now Zed's full combo scales with. I'm not counting in the post-ult damage because it would affect autoattacks the same. What this means is that getting a BT would allow you to deal 412.5 extra damage with your burst, not counting the death mark explosion which adds 50% of that damage on top. Effectively, even in an unlikely situation which would maximize the power of Infinity Edge, you'd still have more of an incentive to build raw AD on AD casters. Ergo, crit would give AD casters less burst than raw AD.