The strobing screen on the screen is related to the T-CON logic which converts the LVDS signal from the LVDS cable to the needed format of the screen at the desired resolution. As an example the higher scan rates (1920 by 1200 (native) can cause this as the Intel graphics engine can't run at this rate. And even the lower 1680 by 1050 or 1280 by 800 can be sputtery which I also see in your posted vids.
You could try using [https://gfx.io|gfxCardStatus] or [https://codyschrank.github.io/gSwitch/|gSwitch] so the OS doesn't assume you have a working discrete AMD GPU.
Even still depending on what you are trying to run you may find the Intel engine is just not up to the task.
I've had quite a few of this fantastic system as I really needed the larger display, sadly each system died from pushing the GPU too far and the software options didn't really work either forcing the Intel graphics engine. I had a long cry when my last one died and had to jump to the 15" retina models.