LA is pretty useful for medics really. A 1 Luck guy with LA will do more critical successes than a 10 luck guy, for example. a 10 luck guy with LA will do about double the critical successes that a normal 10 luck guy would do.
Critical success doesn't matter much if you heal 180+ HP on average and have FA cd below 40s.
And fails are rare, even with 1 luck - if you fail you can try again in 30-40 seconds, because you can heal weak people.
I have two 24 level 1 luck medic builds and crit fails are not a big problem enough to spend additional perk on it.
If I made 3rd build I wouldn't take this perk either.
The only thing I would change would be not investing in lockpicking, because buying blueprints is easier than finding them.
For medic-fighter I think there are better medic perks and better fighter perks.