The exact opposite is true. The vast majority of officiated matches do not have electronic line calling and the umpire has absolute authority to call it as he sees it.
Also, even in the slams, the ump has some discretion over other calls like foot faults, double bounces, time violations, other code violations, etc.
nervouspencil t1_jebb8kf wrote
Reply to comment by Victor_Korchnoi in Tennis umpire handed lifetime ban for manipulating scoring by PrincessBananas85
The exact opposite is true. The vast majority of officiated matches do not have electronic line calling and the umpire has absolute authority to call it as he sees it. Also, even in the slams, the ump has some discretion over other calls like foot faults, double bounces, time violations, other code violations, etc.