The problem here in regards to combo blow is you're using an exotic to strengthen your case, a rare duel exotic at that. On its own it's a good melee option, but it doesn't offer anything too overpowered as far as melees go in general. Combined with your standard exotic (liers handshake for example) it becomes a decent damage option, and this is how it should work. Again, as stated previously it's a risk/reward playstyle. If we take this one step further and you add calibans to the mix you're gaining the explosion which, IMO is only giving you an "add clear option" and seems to me an acceptable tradeoff given that while using this playstyle you're not engaging the enemies with and weapons. It is definitely a strong setup, one I run myself for fun, but in terms of "overpowered"? I don't think so. An example to counter is something like volatile, where a player can proc volatile and wipe out a group of adds with minimal effort and also be at a safe distance while doing so, effectively doing the same job as what the calibans user is doing without the risk of being downed by something in close range either meleeing back or, in the case of many bosses stomping. It's a fun build that combines two play styles and can be very effective in a regular playing environment, however it's not something I'd choose to use in endgame content where he adds and bosses are a lot stronger and harder to kill, at that stage you're only going to run into trouble using it, and it'd be more risk than reward, as stated above due to being hit back or stomped.