There's plenty of shields throughout most of the game, there's just one obvious area lacking - the early/mid level 50 gearing. Shields are a weapon. There should be as many shield options as there are sword options, really. When you ding 50 your progress of weapons goes (roughly, dependant on RNG drops):
Grand Company Weapon / Darklight WP drop -> Ifrit weapon -> Garuda weapon -> Curtana -> +1 Curtana / Allagan.
However shields go:
Darklight WP drop -> Holy Shield / Titan -> Holy Shield +1 / Allagan.
The problem is twofold. There's no Grand Company Level 50 shield that you can buy/grind that guarantees you at least have a green i60 in that slot fairly soon after you ding 50. Secondly, there's literally no shield outside of the super expensive crafted Darksteel Scutum (out of reach for most players) until you've -killed- titan. Which means you have to grind Wanderer's Palace over and over and over until the Darklight Shield drops from its loot table of 10+ items. If you don't get lucky in WP then you'll be using a level 44 shield to tank Titan. The titan shield is supposed to be a stopgap shield between WP and Holy Shield but 95% of paladins will get the Holy Shield on their first ever titan kill, so it's really just a "gear my alts" shield.
Solution? Put a level 50 green shield on the Grand Company vendor that's on par with the Wanderer's Palace shield. This at least will remove the frustration of the RNG WP grind.
Ideally there should be a blue i65 or i70 shield from Ifrit or Garuda but that would give two drops for paladins and only 1 for other classes. You could also implement a stopgap i70 blue Shield and Caster Shield for Philosophy (white mages have a similar issue to paladins if they get the Garuda Weapon because it's a one hander - they're also forced to grind the WP shield although shield slots arent as vital for them and the Ifrit weapon is a 2h).