I tend to like using my bonus action for something else like an offhand attack or hex or misty step, so I use Shadowheart more to heal. Healing wise she has been ok because not much has changed on that front other than food healing now which I am mixed on, and if by some unklucky crit a party member goes unconscious a healing word puts them back up easily. Everyone else does enough damage that I don't feel like I need to attack with her often. Also bless usually lasts at least a round for me that it does end up being useful as my party members benefit from it. But personal experiences are not universal and even when I am using her I have noticed that there are issues with the cleric on their more offensive front.
Also balance can be part of why something is not fun to play, if it feels too weak it feels unfun. If you feel like playing that class is unnecessary to your comp or there is no mechanical reward to it, it also feels unfun. If their abilities do not feel worth using, like sacred flame, it feels unfun. Systems tend to overlap or contribute to eachother.
