Sure some teachers want something done exactly as taught. But more often than not, that is due to the rank/experience of the student. You shouldn’t start changing things too much until you’ve got a good understanding of it.I would also extend and say some styles and teacher are up for more deviation in how you do things than others. so they facilitate you finding your style better. Some would shut down any deviation from the norm and the like.
Also a amusing example i have is a historical youtuber who does HEMA and he literally leans back to avoid swords now and then and it works for him. (given he has a reach advantage sometimes) Kind of that suck in the gut one.
So the dispute there is, why should he stop doing it if it works for him?
As far as why should that guy change what he’s doing even though it’s completely the opposite of what he should do (I don’t know HEMA, so it’s an assumption)? He may very well be getting away with it against lesser opponents and will pay the price against better opponents. I had a baseball player at a college I worked at who was the best hitter I’ve seen. Set all kinds of HR and hitting records. Actually, he buried every record. Despite this and the fact that he was a Div 1 player, he didn’t get drafted. According to a scout that used to come around often, he refused to change his swing. He was obviously too good at the level he was playing at, but the scout said he wouldn’t touch the ball at the next level if he kept swinging like he was. Sure enough he was signed to an independent league team and went 0 for however many dozen at bats. Other than a couple walks, he didn’t reach first base in the 2 months or so he was playing before he was cut. The only reason he lasted that long was he was a very good outfielder.
Perhaps that’s the case with that guy. Or he’s so good at everything else that he can afford to do that. Or it really works for him and no one else.