Crit is always relevant for what it do. It starts becoming less relevant once you hit certain soft caps. If you have a 50% chance to Crit, but one of your abilities have an additional 50% chance due to talents, then you hit a 100% soft cap on that skill. Any more crit past that point becomes less valuable, and raw damage and other statistics would thus be far more valuable.
The more crit you have, the more valuable other stats become for effective damage output, but I imagine the numbers have not been calculated yet. I would, however, imagine that crit stays relevant until certain soft caps or until diminishing returns kick in.
Also, critical hits in this game start at a 40% damage bonus, where other games they go from 100% and up. With the soft cap you mention, and the diminishing returns on the damage bonus It becomes less about the hit chance, but the bonus damage, I think, which is why I am sure mages will be the most promoted class looking back a year from now.
Fortunately, dexterity controls the critical hit damage, which is not infinitely scalable with promotions. Imagine having +500 dexterity from promotions, granting +500% critical damage bonus, then land a critical hit with your Long Shot or Full Draw. Now that would make the game completely unbalanced.