I like this a lot, but please do not listen to anybody who says this path is over powered, it is severely the opposite.
There is the thing a lot of people do looking at Spec's they look at it by itself, and not with the moving parts of the other class abilities. Which given a lot of paths are made on their own and not looking at other class features, I am certainly guilty of that. Also people look at features at where they play at, which is typically low level. But this is a path, it is asking you to give up A LOT of combat utility, which say what you will, D&D is a combat engine. You can do with it what you will, but the rules and focus of the majority of game mechanics are about fighting things. So allow me to explain the bar that EVERY Rogue path needs to be aware of.
Damage Build Level 20 Rogue
Sneak Attack 10d6 - Dex +5. Average dice on a d6 = 3.5
Assassinate, advantage on attacks, and Crit in the surprise round.
Death Strike - a level 17 make a con save (DC should be 19), or take double damage.
So a level 20 Death strike with a short sword is ((22 x 3.5) +5) x2 aka 164 damage on the surprise round.
I hear you now, so thats the surprise round, not all enemies will be surprised. Allow me to introduce you to Expertise (double proficiency bonus), and Reliable Talent (If you roll 1-9 on a skill you roll 10). Which takes that same rogues MINIMUM Stealth roll to 27. An Ancient Gold Dragon has perception of +17, which means it's average roll is 27. The problem is the dragon can roll a 1 to 9, which means that 45% of the time a Rogue can sneak up on a Dragon without rolling.
So that is the bar, a rogue that has extremely good odds of doing 164 damage in the Surprise round, EVERY combat, EVERY time. So saying that throwing out the odd heal for 1d4+Wis is "overpowered" is stupid. Your asking a rogue to give up doing a ton of damage, to throw out minor heals that won't matter at that level.