ramen basically said everything needed to say. but once again, akiba can't blow up all of his allies, and surely there's a defense up dress or something that can block akiba's bombs. not to mention, he only put one per person, and bombs don't one-shot. if they do, that would be a pretty busted subweapon in a game that's designed to at least have some balancing. If they do then Akiba just has multiple insta-kill projectiles that he can spam to his hearts delight, given how he put down at least 15 of them. they also move pretty fast, faster than a character can fly (see adachi, who actually survived a blast meaning they can too).
also worth noting, now that we're entering a battle all the people have to do is wait for akiba to mess up and let shibuya get hit, which would then leave him open to betrayal via knocking him out. dress users can also interact with players as seen with how akiba pushed a player +dress user into a monster (unnecessarily) so they can just slap him around once he feels the pain from the shared senses.
and they can also try to run outside of akiba's range. a significant rangeboost can't mean the whole map, right? Under the guise of looking for treasure they could try to get out of his range. and amputation+healing is an option when he's not looking. the areas the bombs are in are visible and there are definitely sharp object users +healers in the group. so once they inevitably split off to look for them they can carve akiba's bombs out of the people if they truly have to.