I was only to try to help you and in the process it was made some confusions… first, i never say the electricity cut could be the reason for the circle problem.. I speak about this only to explain that the play you are showing in the 3 videos only are happening because the motor are not energized. When all motor have electricity, the play will disappear. To check what i talking, you only need to power on you cnc and make an homing, after this check if you still have any play?
is the play on the axis shown in the videos normal? yes.. i using stainless steel tube, was result i think i have less play, but still have some… And roller that runs using 608 bearings and tubes i think is expected this type of play.
And again, about your circle problem. If you say you do not have any play on the Z axis and your cnc was all corner 90 degree, i put my money that your problem is missed steps. I could be wrong, but i think it will not be a lose of time if you check this by printing an circle using an pen attached to your Z tube. This is an easy and quick test to be sure if is an geometry problem of your cnc or missing steps.