I dont really find Assassin to be unbalanced its just too good to pass up, but as a DEFENSIVE perk it really doesnt help you get any kills, like Quickdraw or Hardline. If you want to equalize the 2nd perk tier then buffing the other perks is a better idea, not nerfing Assassin.

Make uav a 5 assault streak and 7 support and make them disappear once the creator dies. Way less assassin no doubt. Also add higher cuavs in both point streak sections that counter assassin too (more ways to counter uavs than only using assassin and shooting them down). Actually only making uavs disappear when the creator dies would see less of assassin. They can't really balance assassin in this game, support streaks are way too easy to get.

the only problem with assassin is the amount of pro benefits it gives you, imune to port radar/HBS, thermal, no red name abouve you,imunity to CUAV/EMP its just to much for one perk IMHO what i think they should have done is:

Assassin keep you off the radar and the Pro version blocks thermal and remove your name

Dead Silance gets the port radar/HBS imunity

Sit Rep get the CUAV/EMP imunity

this way to get a "full ghost" set up you need to sacrifice all three perk slots and it make what i think to bee 2 of the most underused perks some much need usfullness i mean yer DS does stop sound whores hearing you comming and no fall damage is nice but compared to tighter hipfire and faster ADS movment its really kinda usless in the bigger picture and Sit Rep is made almost obsolete by stalker pro, why would you need to see enemy mines when you can run strate past them.