Xp rewarded for useing explosive devices isent that much. Xp gain is dependent on the type of enemys you are faceing, If you are going against a Tank, harvester and so forth, you will get plenty, but a few hunters or ticks, not that much. Xp co.op wise depends on the other players perks. and there are ways to speed it up by useing Inquisitive mind and veteran guerilla
I tried this yesterday. Two big fights, lots of varied enemies. Blew thefirst group up with rocketlauncher, got almost no XP. Like… A couple hundred. Used mostly SMG and shotgun on second group, and got almost 1000XP.
A very relevant question. Yesterday I killed a hunter (THE hunter waiting at the middle of the bridge going to Salthonen) by a car explosion, and got no xp at all