On most motors there is a c-clip holding the shaft on the bottom of the motor. If there is end-play that can cause vibrations in the z axis. It could be a bent shaft. It could be a lot of things that introduce vibration.
Balancing may not be the problem if an arm is not secured. When I replaced a motor/arm, I checked all the screws holding the arms to the body to make sure there was no side play (wiggling) of the arm. The slightest vibration, or just spinning of the motor could cause the arm to shake. However, the copter's IMU requires vibration at a low enough level to allow it to even fly.
It's interesting even in high wind my H seems to produce decent results. Unless there is some serious mechanical issue causing high vibration, IMO minor imbalances in the props/motors won't be enough to transfer to the gimbal. If the H logged vibration levels it would be simple to see, but even still if vibration was excessive it can cause the copter to crash let alone create poor video.
What settings are you using when doing your videos? I'm finding out that certain settings can create what appears to be jello or even shaking. I agree with others it could be a problem with the camera itself, like an encoder or something.
Today we went to about the only public stretch of beach on Lake Huron that allows horses. My daughter wanted her senior pictures done with her horse on a beach, period. After the photographer was done we had a little fun with the H filming her getting the horse into the water and such. It was quite windy and though he will go swimming with her in lakes, he didn't like the noise and waves. Most horses (nearly everyone I've had) think a small puddle is a bottomless pit and will die if they step in it
Being a rank amateur, I'm still learning how to use the camera settings. In the following video, I did it in raw to experiment, but forgot to lock the white balance, and also didn't calibrate the gimbal after accel calibration and had horizon tilt. I did 3 videos and forgot to set something correctly on each one, but it was a fun day.
This video is raw, no processing. ND4 Polar Pro filter used. 3840 x 2160 30 FPS, 1/250 (IIRC....didn't feel like landing and trying ND8) and wish I set to natural or gorgeous. Some day I'd like to get a 4k monitor.
P.S. I brought the P4 but wouldn't have even attempted to fly in that wind.