It should suffice that you can be proven not to be cheating right here and right now. Unlike doping, getting assistance helps you only exactly as long as you continue getting it.
however, without overly expensive and invasive methods of detection, plus unpleasant rule changes, what you describe isn't feasible. there are too many ways to cheat, and people who are already smart enough to play at a grandmaster level are not only going to find these ways, but excel in them.
I don't have any evidence to back this up, but I would be extremely willing to believe that plenty of high-level OTB cheating has gone on over the years, especially with money on the line
You have to consider not just the immediate effects of a rule, but the iterated systemic effects.