200% of 125 isn't that good when it only happens 20-40% of the time. 130-140 guaranteed damage per auto every second however takes the cake anyday. This isn't even counting how the carry's abilities will benefit from the arpen.
You criticize people of being "hilariously wrong" when you don't even have a good grasp of a simple MOBA concept, Scaling. Crit is only built on adc's so that they scale into late game with their autos. However, flat arpen from items such Ghostblade help them spike faster and have a bigger impact early-mid game, so you end up with scenarios where what even is the point of crit if the game isn't going to last long enough for scaling to be relevant.