Crossguard is my favorite stance and probably my most used one, but it's one of the weakest ones compared to the other ones, in the time you do one attack you can probably do 2 or 3 with dual wield (and let's no start talking about the fact the DW can cancel animations into a block). Usually in other games when you have really long attacks, you compensate by not getting interrupted, like in For Honor you get Hyper Armor, which was my inspiration for this prototype, mainly due to how FH communicates to the player when the armor is active.
I think Crossguard should have had this from the beggining since some attacks are basically unusable in Grand Master due to how long they are.
Keep in mind that this is not equal to i-frames, Force armor would only mean you won't get interrupted but still get damaged, maybe with some damage reduction active at the time and how much damage reduction could depend on the difficulty you're playing.