My shadow is kinetic and level 47. Do you play on The Bastion? I'd be careful about paranoia.
It's an unfair tactic and should be fixed (like jumping over the gap in VS, which was fixed), but they are just using what's available to them. Exploits are more serious than that, like planting from inside the wall or abusing the old Voidstar ramp. Where something is clearly going wrong. Placing an AoE doesn't qualify on that level.
Edit: Nice try editing out your accusation.
From Wiki: An exploit, in video games, is the use of a bug or glitches, rates, hit boxes, or speed, etc. by a player to their advantage in a manner not intended by the game's designers
So yes, i thinik it would be considered an exploit unless you mean to tell me that the devs intended that kind of usage...