Power breakdown mid-flight

We can not takeoff, motors can not speed up more than %50 throttle. Power is waving like sometimes it gets faster and suddenly slows down. When we get in the air by luck, power is gone in mid-flight.



It seems like we can not exceed 1500us. RC is calibrated. Tested in other quads.
PDB replaced. Pixhawk replaced( Pixhawk 4). Nothing changed.
Motors: sunnysky 4108 380kv (quad)
ESC: https://www.roboshop.com.tr/30a-2-6s-simonk-esc
The build is around 2400 gr. This setup should lift 7 kg (8kg lift at the max throttle)

What could be the problem?