One last point...

A well timed BR wastes absolutely no time at all. Not even a fraction of a second.
Take this example:
2 exact characters... same stats, same gear, same class, level and rank....

Character X spams light slash until his stamina reaches zero... and keeps spamming so as soon as he has enough stamina to do another light slash, he does

Character Y spams light slash until he is out of stamina, but then waits the 10 seconds for his stamina to refill completely. The instant his stamina is full, he resumes spamming of light slash

Freeze frame the second Character Y has emptied his stamina for the second time. You will notice the 2 characters have done the exact same number of light slashes....

A good BR works the same way.... yes you can't attack for 3 seconds... but no stamina is wasted... once you get done, you can launch several attacks in succession and build TP again relatively fast because your stamina gauge will be higher
No actual stamina is lost.. I repeat NO ACTUAL STAMINA IS LOST as long as your BR doesn't take a long time
I was able to tank all pre-patch NM's just fine while participating in BR, as were the healers in our party