ok, so you're all aware of the more powerful grenades and faster grenade-throwing that soldiers have, right? Also, you're aware of the medic's adrenaline skill rendering someone invincible temporarily with a yellow outline?
I played a few games where, and this seems rare still, all the attacking team does is adrenaline-buff a few soldiers then the soldiers power-nade every defense they see. It feels like tf2 ubercharged demomen. Either two power-nades or one and a few shots renders turrets worthless, adrenaline can only be countered by knocking the enemy down, but the grenades they throw are such quick, single attacks that can go anywhere! It's like nothing you do matters...
If anyone else has seen this... it seems a few trends are growing here and there and may go from rare to popular.
Sounds to me like you just described a great tactic, not an exploit. Also, I never really thought of this until you said it. Now you've got one more medic adrenaling the hell out of soldiers.

In all seriousness, adrenaline isn't THAT overpowered. As said before, it's short duration, long recharge, coupled with the fact that the target recieves all damage when when the effect wears off, makes it fairly balanced. So keep shooting at an adrenalined enemy, then run, because they'll die moments later.