The only issue I have with PLD gauge (can't speak for the other two as I haven't leveled them yet) is that it builds VERY slowly in Shield Oath while fighting bosses.
Yes I know that I can use Holy Spirit spam to fill it, but it just doesn't really make sense why I can build gauge by dealing damage in Sword Oath, but not taking damage in Shield Oath. I have to BLOCK the damage.
Not really a huge issue either way.