What they need to do with the shields to make them viable is to make them oGCDs, without heals. Gobskin by BLU is a good example of a good way to do shield healing in the future. Instant cast shields for use whenever, but we'd have a cooldown. This would allow them to merely change the current heals to also give damage mitigation for the next 10-15 seconds to continue the shielding in a fashion.
Examples of some changes to encourage shielding:
Succor gives a 10% damage mitigation with the AoE heal
Adlo gives a 20% damage mitigation with heal.
Emergency Tactics gives a 20% max HP shield along with 20% damage mitigation.
Deployment Tactics giving an AoE 10% max HP shield along with 10% damage mitigation.
Lustrate becomes a (up to) 3 charge oGCD that gives a 20% max HP shield.
Fey Blessing becomes an (up to) 2 charge oGCD that gives an AoE 10% max HP shield.