Is Hex worth it at high levels?

[diplomancer]

If they're taxes, then, does that mean hex is just not worth taking as it is? Or are you just saying they're too strong?

Hex on a fullcaster at higher levels is niche. Even more so for a Warlock, considering how Pact Magic works. I wouldn't go as far as to say it's not worth taking or a trap, but its uses are limited. It's still a good option for a Martial who takes Fey-Touched, be the martial a half-caster or, even more so, not a caster at all... but this is because all classes are encouraged to use their "Concentration slot" on something (by the way, and I've just realized this, there's unused design space for martials there).

With this invocation, Hex becomes quite powerful even on a single-classed Warlock... a straight, almost cost-free, damage buff. It's comparable to Agonizing Blast. Slightly less powerful damage-wise but applicable to more damage sources than just Eldritch Blast. And Agonizing Blast is pretty much considered an invocation tax on any Eldritch Blast-based Warlock build.