I meant to ask this a while ago, how would Conjure Duplicate interact with other personal illusions in your mind? Such as the Firbolg's Disguise Self (or basically, the spell)? Would your duplicate look like your glamoured self, or your actual appearance? Could be useful either way.
Treachery seems pretty nice though. Lots of ways of generating advantage and nice damage boosts available from it. Good spell list too. Even the capstone is worthwhile. At worst, unbreakable invis for a minute is a lot better than some other capstones, but it can come with +20 damage an attack for a minute (or +60 with divine poison for one attack) for great damage burst, as well as "don't hit me" utility.
Also, for rules lawyering, since "creature" can be yourself, and you are within 5 feet of yourself (for things like spell casting at least), and that goes for other creatures too assumedly, can Treacherous Strike be used to make a creature stab itself? RAI probably not, but RAW maybe.......
I might be thinking of PF definitions for stuff like that. They could probably insert "another" or "different" into that sentence to avoid any rules lawyering. The word "also" probably covers it, but not well.
With the hugely varying power of different abilities for classes at different levels, it really is hard to tell just what is intended rules-wise in 5th.