No because then they would need to buff the HP of all content to balance for the fact that everyone would have their own LB, which would be additional free damage. Secondly it wouldn't make anything easier because of the aforementioned rebalancing, so it simply becomes another cool down to manage. To that end, what would be the difference between giving a DPS their own DPS LB vs giving them a powerful oGCD with a long recast, e.g Dragon Fire Dive, or Contre Sixte or Midare Setsugekka? Those are powerful skills on cool downs, why can't you just imaging that those are "LB"? Or do you want actual skills with a cast bar that do high damage? Again I don't understand why, as it just becomes another thing to manage and use off cool down, another button to press, at that point it just becomes another cool down to use 1 or 2x per fight. Instead just think of Natrond, Contre Sixte, Midare Setsugekka, and other powerful cool downs as "LB"