If you take away shields you'll break the viability of WHM/AST groups on a lot of Savage content (which is already a rare combo, but is totally viable) and you'll make ultimate basically impossible since the boss will just kill everyone without heavy party mitigation management, which pugs will be really hard pressed to handle. Having cards handle debuffs is not gonna help because it's RNG.

Direct heals also tend to be GCDs , and the over reliance on GCDs is a big part of the reason why WHM is ignored in meta. It would be extremely interesting though to replace benefic/helios with weaker insta-cast oGCDs that you could weave using some kind of resource (or we run into even worse mana problems than we already have) , so you'd really be speedy in responding to damage. They could get the trait from ED that increases the potency the lower the target's HP is so there is incentive to AST always being the first to respond.

Resource generation could be tied to your card play so you don't just hold stuff forever, like the faster you deal with the card the more you build kinda thing, and using Minor Arcana on it could punish you by generating less of this resource that you need to cast insta-heals.