i play on PS4 and have the LB button on my hotbar, and i am a tank who basically never uses LB, so space shouldn't be a problem...

in the rare case i play a DD i often simply forget about the LB, because i am absolutely not used to use it. but i try to improve. and also use it between 1st and 2nd boss, but mostly i play melee when i am on DD, so that's not my turn i guess... but i have used melee LB on trashmobs with a lot of life, like the first trashmob after the first boss in the lvl 67 dungeon.

i think because the LB is a shared ressource, people are worried to use it (and i have seen people got called out because the party wanted to save it for the healer or a specific mechanic).

when i see people using the LB then usually at the last 3% of the last boss and until the LB cast is over, the boss is basically already dead, so the LB is wasted. so please use LB at 15-10%, okay? ^.^/