I too have been in the school of thought of arbitrary choosing of point-of-contact - and I'm almost sure they still guess the frame to choose since you sometimes see them flicking back and forth. In addition, they are heavily limited by camera frame rate, which I'm guessing is capped is capped at no more than 60Hz. This means ~ 0.02s is between every frame. That's a long time when considering two bodies can be moving in opposite directions at 8m/s each - 30cm in fact can open up in that time (and that's discounting possible leg extensions being pulled in at a much quicker speed)Actually I think you are wrong on that these days. I used to think it was arbitrary in regard to when the ball was kicked but I'm sure I watched something before the World Cup that explained that is no longer the case and that the match ball now has a sensor built in. Here's an article...
The World Cup’s New High-Tech Ball Will Change Soccer Forever
When the 2022 World Cup made its debut on Sunday, it kicked off one of the most significant in-game uses of technology in sports history. All tournament long, m…fivethirtyeight.com
PS. It is "offside." A singular event.
Until they get 240Hz cameras & monitors as standard, I think the onfield decision should stand (unless a clear mistake has been made, i.e behind the half way line, not the actual last defender)