Posture recovery being tied to hp is an immaterial difference IMO.

Leveling up being based on finding/fighting new stuff rather than how many souls you sat down with is still leveling up.

Sekiro being the least souls-ey of the bunch is a free argument. It not being one at all I just won't buy.

You do spend posture defending and attacking though. The only time you don't is if the attack doesn't connect.

You can absolutely stagger every enemy that blocks in dark souls/elden ring too. In dark souls 2 it's even one of the safest ways to riposte, by doing a guard bash.

Combat absolutely is based around stamina management. They just called it posture.

The game has a level up system. You gain actual exp and actually level up. Exp lost on death.

Stat based leveling is achieved through exploration and boss kills which is every other souls game but with less steps.