I didn't say that. I said they are worth less because there are so many. In football for example the difference between 1-1 or 1-2 is huge, and decided by only one call. There are hundreds of points in a tennis match and thus, manipulating just a handful has a much smaller impact overall.

If an umpire makes regular hard overrules on vital points multiples times in a match they'll be under a microscope in no time. There's no way they'd get away with that if you want to affect more than one match

That's true, but points in general are worth way less in a tennis match because there are so many. The ump can't manipulate too many or it'll be noticable, nor can he really do it on the very few truly vital points withouw drawing major objection and attention. Best he can do is do it at opportune times and hope it takes one of the players out of their flow. It must be very hard to make it work in any serious way