Name of this genre?

Third person Hack and Slash/Action games or RPG in the case of Witcher 2

You stole space kitty

We used to call them Action Adventures, no? Witcher is an Action RPG. Ninja Gaiden and God Of War would be examples of Third Person Hack n Slash.

I don't think such a fight mechanic is defining a genre (at all).

The ones mentioned happen to be RPG-ish, but the description of what you asked
for would also apply to arcade style fighting games like streetfighter or nidhogg for e.g..
I'd say it can even apply to some card games.

So would it be best if I classify those games under action adventure then?

The fact is everyone refers to Batman Arkham series when they think about that genre, so they always just say "combat system like Batman".

I would say that "Third Person Hack 'n' Slash/Action" (by SirIroMaiden) is a good definition, but to make it clear, you should say "à la Batman Arkham Asylum". That would make everyone understand what you are talking about, except for those who never played the Batman series.
They occasionally have Stealth and RPG elements, but I don't think they are crucial to define the genre.

As others have pointed out it could be Hack & Slash, ARPG, Action/Adventure, even Fighting or Beat 'em Up/Brawler depending on the game. Also consider titles like Chivalry: Medieval Warfare or Warhammer Vermintide and where they would fall. It doesn't seem like the criteria you have set is going to fit neatly into any one defined genre.

The games would fall under 3rd person action (or action adventure) with several of them containing stealth game mechanics. The actual difference between the types of games you listed and other 3rd person action adventure games (Resident Evil, Diablo, Super Mario 64) is the focus on the close combat system which can be termed whatever you deem appropriate (active counter combat system perhaps?)

Action, hack + slash, brawler.

Ohh, I would like to know how you guys category them in standard Genre too, this would help me write description better.
Genre nowaday really confusing I would say, especially RPG one. So does RPG mean the progression system (level, item), create-your-character/story or You are 'Character' in the game (then again most game now have story in it), or whatever that justify RPG genre?

"attack, counter and parry" are more like a game mechanic rather than a genre. But then, sometimes a genre is defined with the mechanic of the game (like FPS, or platformer).

IMO, the gaming industry have a very broken way of defining game genre.

I recommends watching this video. It talks about game genres.
https://www.youtube.com/watch?v=uepAJ-rqJKA

The fighting mechanism itself not defintes a genre, but all of the mentioned would fit into action-adventure, or similar category, or you can label them with RPG as well - RPG is such a lazy definition nowadays that you can tag it on almost anything, everyone interprets it differently :)

I would call it Open World Action RPGs

This is of course subjective.

But these are actually all 3d/fp action games as I see it, with heavy combat elements.

Games that have combat as the primary feature and you end up playing more than half your hours on doing combat with so much heavy button mashing, are pure action hack n slash games in my book (and a genre I personally almost loathe).

However the Witcher franchise is probably one of the very few exceptions to the rule, since it tries to balance many things including story rpg elements and even open world (especially in 3rd game not so much in the other ones). However you still end up doing too much combat in these games too. So it's a hybrid of the two genres as I see it. Something in between. The rest of the games mentioned are much more toward the hack n slash type of action games, don't expect rich stories in those. You literally only play them for the action/exploration part.

Assassin's Creed franchise

Action/adventure

Shadow of Mordor

Action/adventure

Batman Arkham franchise

Action/adventure

Mad Max (ground combat, not vehicle)

Not played yet

Witcher 2 (I'm assuming Wicher 3 as well but have not played it yet)

CRPG

While all of them are 3rd person, have strong action elements, and character progression, I feel that only The Witcher 2 puts a heavy emphasis on the RPG element, where it's deeply entwined in the core gameplay. For AC, even AC Unity which has exp-based character progression, Shadow of Mordor & the Batman games, I don't feel that the RPG-elements are a core part of the game, and removing it would not greatly impact how the game works.
So I don't think you can lump together these games. You can probably apply "action" to all of them, but it will be action-something, not just action.

Action Adventure besides Witcher 2 which is an RPG.

You're talking about the combat system, not the genre. Usually action games have similar mechanics

I have Batman Arkham filed under "Stealth"

I always thought that Batman Arkham Asylum was closer to a 3D metroidvania than anything else. But Arkham City is more of an open world game.

If I need to use one word then I go with Action (exept witcher - RPG).

I haven't played Mad Max or The Witcher, but the others are very similar. I'd probably call them hand-to-hand combat/climbing adventures

Third Person Action/RPG. To me, nothing even close to adventure.

I'd call them third-person action. Hack and slash makes me think of games like God of War.

if you had to throw them into a bucket I'd say they fit Action adventure

Personally, I would put AC and Batman franchise under the "action stealth" category :)