Everyone goes on about the 30cm margin of error that someone once calculated in a newspaper a year or so ago.
This solution a) ignores that and only uses 10cm thicker lines, which is a negligible change and b) does nothing to solve the issue of the fact that there will still be decisions that miss the margin by an "armpit" or where the judgement of where exactly to place the mark that lines are drawn from is still extremely subjective and looks right or wrong depending on which team you support.
Not showing the line drawing process is a definite improvement, as it can only ever look like the VAR is trying to produce a particular outcome! A better solution would be to place the attacking line and the defending line on two separate pictures, then superimpose them after the position of those lines is locked, as that removes even subconcious bias from the VAR. For example, using the new overlapping lines system, there will be a certain incentive to make sure the lines overlap and support your friend and colleague's decision. Marking the second line without being able to see the first would make that harder, meaning more honest and consistent results.