Completely agree with you.
I took a little break from Arma3 for 1-2 months, I decided to play today again after I saw there were some updates. And what a surprise, MP is unplayable now for me. I'm part of Arma3 since alpha, even when everyone was complaining about the bad performance in the first few months it came out, I had none, I had 50-60fps almost constantly in MP (I mostly played on servers with +20 players) and more than 100fps in SP, and now I have max. 30FPS in MP. I can put the setting to the lowest or to the highest it's stuck between 20-30FPS, and keep in mind I didn't touch the game for 1-2 months and I didn't change anything to my computer.
My specs:
GPU: GeForce GTX 560 Ti
CPU: Intel Core i7-2600 CPU @ 3.40GHz
RAM: 16GB
Running Windows 7 64-Bit