Yeah, that’s since been debunked as a myth. Crit and AP both have the same decline as suggested in the graph they have, and they’re both linearly related to each other. Meaning per point of AP, the damage added from crit increases by the same amount at a given amount of AP, and the damage added from AP increases by the same amount per point of crit for a given percent of crit.
This means that if you were to stack 1000 AP no crit, adding 1% crit would be worth 50-60 AP, or having 50% crit, 500 AP, and adding 50 AP would be worth a lot more than just 50 AP.
The bottom line is there is no “breakpoint or soft cap” where you want AP over crit or vice versa. The stat weights change based on your gear; higher AP means more value from crit because you hit harder and crit harder. Higher crit means more value from AP because you crit more. There is a hard cap due to gear/enchants limitations; however, around 64%.