I agree mate. Yet 5 seconds is just too little of a 'brace'. 10 seconds would be reasonable in my mind. How about yours?
My opinion is 3 second duration, 7.5-10 second recharge. (4.5-7 seconds inbetween Braces.) 7.5 second recharge would literally just be 10% of the live duration and recharge.
I think short duration, short recharge is preferable to longer durations/recharges. Shorter timers increases the burden on the British faction player. But to be perfectly honest, I have no idea what will actually be best. Brace has been a contentious ability since it was released, and it's caused a litany of issues with how the game has been balanced. This is something that will have to be toyed around with.
IMO a change to brace warrants its own mod. One change for the whole thing: Brace. Otherwise it'll be more or less impossible to determine what is best.
And to go further, I think the whole British faction needs to be scrapped and redrawn from the beginning if they are to fit into CoH2 in a balanced and well-designed way.