Sure, Hex has other applications besides damage, but damage is the primary one. And Agonizing Blast is more damage than Hex, in most situations (usually 4 or 5, vs. Hex's 3.5), it doesn't take any actions, and even without the invocation you can still use Hex sometimes if you want. I think all of that more than balances out the check-disadvantage rider on Hex, to mean that this Evil Eye invocation would be less of a "must-have" than Agonizing Blast.