Eh.... I'm not sure about that. You can get extra mileage out of it with with accessories for beneficial status effects but I wouldn't say you cast less often or anything. The thing is, between Lifesaver and Manawall - your group is going to take WAY less damage and spend far fewer actions dealing with the damage that they do take.
Healing spells heal HP based off the magic stat too - Barret can heal, but using Curaga to do it just isn't cost effective. Pray and Chakra do healing proportional to the character's HP and the level of the materia itself. Its just the better option for Barret overall imo.
Refocus does give a small flat boost to all stats for that character, true. But it also pushes your ATB Meter from 2 to 3 for the rest of an
entire fight which is huge. A limit break is there and gone and better be well timed... Refocus gives you crazy options and damage output over the course of a fight AND you still have your limit break when it comes around again. In normal mode I was using it with Tifa and Aerith to do stupid damage (Triple Thundaga x Magnify?

). But in Hard you can basically always have cash in the bank to heal, buff, or throw in damage you wouldn't be able to otherwise. Its really, really useful when managing status ailments too. There's nothing worse than picking which character to save when your whole group gets hit with a status effect.
Elemental damage on Barret helps for fights like that too because he's always going to be shooting the whole time. The challenge in that fight is keeping Cloud alive to the last stage where Cloud can finally freely do big damage.