I really don't like the sound of this.
Stamina to me has always been a big no no as it just restricts gameplay. It may work in a one on one where you can manage it but fighting multiple opponents for multiple minutes in a battle situation just sounds horrible.
The new stances sound terribly restrictive as well, you cant perform an attack if you don't have the correct stance, once again may be fine if your in a one on one but in a battle situation where things are constantly changing and your fighting multiple opponents at once, it doesn't sound viable.
It sounds like this combat is geared towards duelling type gameplay and not the hectic situations of a battle environment.
The reason m and b combat is so good is that it has a basic 4 directions that you start with, every new player knows these directions and can use them from the start, its a very easy idea to grasp. To make the combat more intuitive they didn't add a bunch of gimmicks, they added functions on top of the 4 directions like chambering hilt slashing etc, but didn't mess with the core mechanics. That's why it was still accessible for newcomers and engaging for veterans.
However your approach seems to be just adding loads of things on top of each other to try and create something new and intuitive and yet still easy to play. But to me it sounds like it will be the opposite.
I got the same initial impression as well. Stamina usually makes things worse, I'd understand it if it was just used to prevent endless spamming, but there are better ways to do that. And I fear this stamina system may have a huge effect on one-vs-many or even many-vs-many battles since there's one more factor to watch out for. Especially if it takes too long to regain that stamina. It may just add too much for complexity imho.
Stances.. I've kind of conflicted feelings about that. If it's designed to make life easier for newbies.. then it kinda makes sense. On the other hand, the beef in these kind of games is learning all about the combat and the freedom of attacks. Teaching newbies to lean on some helper stances just feels like a step back in long run. I didn't quite get it how to assign/change a stance so I'm also worried about accidently fuck up and get locked into one.
It's hard to say if these ideas feel right or wrong without trying them out. I'm a bit worried since it's a lot more complex than the initial ideas. Still, what matters most is that the combat itself is fluid and feels responsive.. even if it didn't offer anything new to warband's combat system.