Is Hex worth it at high levels?

[diplomancer]

When I played a warlock, I didn't, in fact, take Agonizing Blast. I probably would have eventually, if I got high enough level, but there were enough other good invocations competing with it that I couldn't justify spending one on just "more damage".

An invocation that lets you use Hex where you couldn't otherwise is worth about the same amount as one that lets you add Cha-mod extra damage where you couldn't otherwise. So it's no more nor less of a tax.

But there's another functionality to Hex besides damage, that, without concentration and paired with some particular spells, can be very powerful. For instance, shifting a Hex into someone, targeting their Intelligence, while simultaneously casting Phantasmal Force, can easily take someone out of a fight completely. Fail the first save, and now you need to make a check with disadvantage to get out.