This umpire is known for penalising players when they break the rules and not letting things slide. His record backs up that nothing about his choices yesterday was unusual. He’s penalised male players plenty, including in Grand Slam finals. Rafael Nadal’s gotten more penalties in matches from this umpire for far more minor infractions.
Serena was breaking the rules. That’s not in question. Her coach was being very blatant about coaching her. It doesn’t actually matter if she didn’t see him, since he’s her employee and her responsibility, but she clearly did see him because she did exactly what he gestured at her to do immediately. He also told the press he coaches her on every point. They’ve been together for years, so it’s not like he’d be bothering with the constant sidelines coaching if she never pays any attention to him.
After that, she smashed her racquet. Had she not already received a warning she probably would have got away with that, but once you get a warning that’s the cue to be on your best behaviour basically, and instead she almost immediately committed another violation.
Then she went off on the umpire. Umpires have been called worse, yes, but rarely right to their face like that. Players who mouth something ugly or say something about the umpire to themselves or their team often get away with it because there’s usually a little bit of deniability there. Umpires also rarely care if players swear about the penalty, say fuck off or whatever under their breath etc. But if you call the umpire a thief and a liar and threaten their job to their face, you’re going to be penalised, especially after two other infractions. You can get frustrated, you can argue, you can make it clear you think it’s a BS call, but you don’t get personal to the umpires face.
As for the McEnroe comparisons, he was penalised a lot, but the rules and standards have also changed a lot since he played. Plus he was always considered a ridiculous, whining, ragey jackass, even by the fans who loved his game and found his lunacy entertaining. If Serena wants to be thought of in those terms then that’s one thing, but she clearly wants to be thought of as a role model.