I remember that the purple node in PvE had a decent chance of dropping experimentals (purple/epic) when I first started playing. Now … I haven’t seen a single purple (I even got faction papers, wtf?!) in over 50 PvE games, only uncommon (Military/Green spec).
I believe the way it works is like this: For whatever level of PVE you’re playing, the dedicated loot drop is going to be either a purple of that level or a green of the next level, or something like loyalty reward. So if you’re using T3 ships, you can either find purple T3 or green T4 equipment. It seems to be heavily weighted against purples, though.
Also, 4 of the last 5 PVE games I’ve won, I’ve gotten loyalty, which is lame.