I've been in numerous server top 5 guilds, and even a top 50 world guild in WoW raiding- playing with excellent players that know their class inside out, the raids inside out and ways to excel, many of whom parse constantly in the 95-99 range. Want to know how most of them give advice to pugs that are bad or trial raiders that mess something up? 'Uninstall and kill yourself'. Toxicity and elitism go hand in hand. There's some of them that can be relied on to explain how to do mechanics or play a class well and give detailed feedback after raids- others that despite being very good generally respond to mistakes with swearing and telling people they suck (albeit in a considerably less pleasant way)- and after saying something like that when the target leaves group or gquits they're always shocked that their polite 'advice' upset the target. In my current guild I've seen at least a dozen decent players leave in the past year solely due to a single mistake that resulted in a stream of 'polite advice' that other members of the guild couldn't believe could offend someone.
And it's the norm in big guilds and top players, it's basically the systemic toxic culture that has become how elitists simply act in video games. Passing off insults, threats and the such as 'polite advice'.
So it actually is a gigantic leap in logic to assume anyone good at the game both can explain within the few minutes of a pug run to someone who they know nothing about how to be better, and that they will do so in a way that's helpful and polite. Perhaps if I hadn't spent over a decade playing MMOs where so called 'helpful advice' is nothing but insults almost all the time, resulting in groups breaking up, players leaving guilds or quickly escalating fights breaking out- I might be inclined to believe the army of good players that claim they only ever give polite constructive criticism. But for every time I've seen someone give good, polite advice in a group, I've seen a hundred players tell someone they suck and to delete their game. That's what makes it such a leap- it's not something backed up by what actually happens in online games.
If you want to give good advice and can do so, by all means go ahead- but if you're in a situation where you're constantly finding players consider you rude, maybe you just aren't as good at giving polite, constructive criticism as you think you are. Or perhaps it's the fact that players can see right through you and that your elitist way of looking down on others makes it very clear you have no intent of actually helping them and use 'polite advice' as an excuse to show your disdain for those you consider sub-par.