I beg to differ. Demeaning a person, or not, on an individual basis is a question of civility and etiquette, which is an individual choice. That, however, is not slagging a person via group affiliation, which crosses into the realm of "politics," in the form of what the wider society has deemed unacceptable. I'm sure you can see the difference. If not, let me make you a clearer example. For Rosewall to say in public that Thiem was disappointing was merely a comment on Dominic, individually, and how he played. Everyone can decide for themselves if they thought it crossed a line of etiquette or appropriateness. Had he said, however, "Thiem, like all Austrians, played disappointingly under pressure," THAT would have been politically incorrect, as he would have been demeaning a whole group, and demeaning Thiem, not for his individual performance, but simply because all Austrians fold like a cheap tent, in his estimation. Does that help?
As to what commentators say and don't say in the course of their hours of palaver during tennis, that is another question. They are contracted by networks, and we can see that there is little room for real individual opinion. This is a wholly different question, and has nothing whatsoever to do with the notion of political correctness. It has to do with appealing to the masses, assuaging the nerves of the big brass against loss of viewers/ad revenue. We can see they let a few loose cannons in, like McEnroe and Wilander and Becker. And what happens? Everyone here hates them. But they're there to spice it up. It's all a calculation, and it's all but scripted. That's TV, not PC.