the problem isint its high power - that is manageable - the problem is that its the strongest move in the game. and it heals 75%. boomburst doesn't have viable users even with its usage, since the best one that gets stab is exploud which is only mediocre in the meta. the problem is when you get a poke with the power and speed of heliolisk, and then add healing from the game's strongest move, and the result is a move that is really overpowered. slap on a choice scarf and its a revenge killer than can heal hp it loses from SR etc. slap on a choice specs and watch everything die to your power. people will even run bulky sets and say only thousand arrows can ohko and if you don't i'll gain all my hp back. Thats pretty simple and easy to use, and doesn't require skill whatsoever. you are taking exploud, which is viable, and you are adding more power and speed, one of the best attacking types in the game, and it healing the user a large amount, you have one of the strongest possible threats in this meta.