Hm...offhand?
LB1: Heals party members for ~1/3rd of health and grants them a weakish barrier for ~5% of their max HP (or this can be potency based, whatever); stacks with other barriers. Also restores half the LB gauge on use. (One of the big reasons we don't use LB1 is in most content is because we want to save up for LB3s, so refunding some LB gauge could make this a more useful thing since you often get a full LB3 use and some change for an encounter, so this could still lead to an LB3 use.) ALSO, some way to allow the player to use to use LB1 even if the gauge is more full (same thing; maybe you have 2.5 gauges but you could use effectively half a gauge for some party healing and light mitigation at a key moment).
LB2: Heals party members for ~2/3rds of health and grants them a weakish barrier for ~10% of their max HP, and grants them a Regen of some good potency. (Not sure if a gauge refund on this one or not.)
Oh, and shorten the cast time/animation of both. It's silly long for how pitiful the current effects are.
One thing they won't do but could is put a Reraise on...something. I feel like LB3 should grant a Reraise for a short time (30 or 60 sec) and LB2 could then Raise but to a weakend state (LB3 Raises to full HP and MP, grants Reraise to anyone NOT dead at the time). I feel like there's some ability that works that way in...some game. Maybe...oh, Remnant 2's Medic ultimate, that's it. I think it works that way. Raises if a person is down, gives Reraise if they aren't. But that would be LB3 probably.
.
Right now, 1 is a total waste of a LB gauge since you can easily heal that much with most of your powerful oGCDs or an oGCD plus a GCD. WHM can probably use Plenary Cure 3 or Temperance Medica 2 and get a stronger effect than LB1 (OR LB2, for that matter...). Power creep has made it to where our standard spells are probably as or more powerful (or at least comparable) to the healer LB1/2s at this point.
They need to do more than just heal, and especially LB2 should get people to full health and give some kind of insurance against following damage (so either barriers or HoTs or both). Again, otherwise you can outheal that with just standard healing spells at this point, making them kind of entirely pointless.
.
EDIT:
Honestly, it makes me think of the "Nova" system in that Kingdom Hearts mobile game (Union Cross?). Early on, it was this powerful desperation/limit break type attack. But by the end of the game, it was an ABSOLUTE waste of a turn considering even your base attacks did more damage and there were Supernovas and Renovas (refresh your Supernovas for an additional use) and you could chains of these ridiculously powerful attacks and your basic, non-Supernova attacks were more powerful than the Nova attack, which would often do 0 or 1 damage due to enemy armor/defense scaling over the years-long run the game had.
That's how I feel about Healer LB1 and LB2 at this point.