Oh, my idea is to make their bonus action “You are my prey” feature be the Search action, with a special thing where a successful check lets you add a flat bonus to your attack rolls against the target. Consistency over damage, and then have the smite-like spells be the main damage boost option, but with the downside of using up resources.

Tbf, Feral Senses is also pretty much an optional Warlock feature, arguably Warlock’s one is better and at a lower level. Truesight is better than Blindsight unless you us the Fog Cloud spell or get Blinded often.

Half-caster Warlock is a scale model of the martial-caster divide. They could put almost any level 18 or below feature as an Invocation and people would probably say it’s worse than Mystic Arcanum at that level.