Ideally you want the worst-geared (or worst-performing) DPS in whatever LB you're using to be the actual LB user. LB damage is based on the average weapon level of the entire party, so it's just as strong when used by the (say) i50 DRG as the i90 DRG.

Additionally: if you have DRG and MNK, DRG should be the one to use melee LB. SMN should be the user if you have both SMN and BLM in most cases (some exceptions; BLM is more suited to using it in Titan EX if you do that, due to Manaward and Manawall). Both of these jobs have "filler" downtime (Ruin spam, Full Thrust combo) where their counterparts would be better off continuing their time-sensitive rotation.