You need to do something about Boomer cuz he is the most useless hero card in game (probably). Do change on his stats 100hp less and 100 on attack, add more % on attack skill, reduce defense against holy and add new skill (dispel ailments all allies, or add poison dmg per turn, mana regenaration, defense on all allies) just do something to balance this hero card.
I agree that Boomer is trash
However, what is SG motivation to fix him? He is in a portal which contains a fair bit of trash (looking at you Sargasso), but it also contains Finley. People are going to pull there because Finley is one of the most overpowered chase cards in the game. They don’t want to make every hero worthwhile otherwise it means less pulls are required to get the chase cards
Look at the upcoming guardians. Some good stuff but diluted with trash they don’t bother fixing, like Owl. Same all over. Hide a few chase cards in there and make the remainder ok to poor. Basic maths then means you’re even less likely to get the good stuff
Kasshrek is a healer itself. I think Boomer should have an Element Link that heals some undispellable HP over time for all Dark allies including himself. I think this would be a good fit. He’s a Dark hero that gives DEF against Holy, so it could also add strategy/fun along with some balance
Only HotMs get element link.