I agree that friendly fire would fix a lot. And jackal was OP before the other nerfs, but I didn't think the Jackal was OP as of the last patch. It was way OP at the very first outside with the ability to tear people up with midair explosions, but the radius and damage was cut way down (with an extra -50% if it's not stuck to a surface before you detonate) a long time ago. Now the jackal projectiles only do 400 damage - stealthfuser still does 700 and bigger knockback. I believe the arx buster is 600, so that's 1/3 less damage than the nearest equivalent weapon (which I never see anyone using anymore now that their other guns are so much better).
I've been using the stealthfuser since the patch and doing way better with it than I was when I tried the nerfed jackal. Two quick direct hits and a medium is down, three if it's only splash damage. Jackal I'd need to land 4 shots direct, and a miss usually doesn't do damage due to the fact that most folks keep moving during a fight so by the time you've fired all three and detonated you usually only have a chance of hitting with the last one if you missed all three. And ammo - jackals burn through their ammo way faster than the spinfuser or smg. Post-nerf Jackal is just inferior for medium killing. Plus the way the jackal rounds just disappear without exploding if you die kinda sucks too, at least the spinfuser if I've fired before I'm dead I might still get a kill, on the jackal I have to fire and reload before anything happens.
Everyone cries over the infiltrator being able to one shot mediums, but it's only the idiots that stand still - folks who keep moving are very difficult to get all three of the projectiles on. All three heavy classes (which the infil is most often facing to do things like clear a flag stand or blow the gen) have weapons that can one shot infiltrators (and the mortars can one shot medium suits too). Friendly fire would really fix the mortars, though - right now you can mortar spam and earn tons of kills without any worry of hitting the half dozen teammates standing where you're shooting.