This isn't currently an issue, because although some healers are referred to as "shield healers", you do not have to play them as that in hardly any content and it's not considered optimal to do it either. If you use shields you spend a GCD on something other than damage, when there is usually a heal alternative that is off the GCD and doesn't interrupt your damage.

On astrologian, shields are seen as less overall healing than regens. You could even say that it's the reverse problem in this game and it's more effective to just throw a regen onto someone than a shield because both of them expire. You could even say that off GCD healing has overtaken healing and shielding altogether in a lot of content.

So right now it's not a problem but there are similar problems with other types of healing, but shield healing might be something in the next expansion. In the next expansion, fights will be designed to consider that one of the healers is a shield healer.