I like that you are saying personal skill in lower ranks is more important (Wolfie take note). Because that is what I focus on. Improving myself as a player.
Criticising players, whatever the intention, shows that you think you know better. Being deliberate arrogance, or just a subconscious thought. It is irrelevant.
Mistakes happen. Sometimes people don’t have the skill to pull off your suggestion. Some times they have a style ingrained into their mind and no matter how many times you say something, they won’t change. And that is why they get stuck in their rank, or fall back.
Where as you might learn, evolve and improve. Thus your MMR will go up and you will slowly climb.
the mistakes made might cost the fight, or even the match. So be it. They will not cost you your MMR (unless it is you repeatedly making the mistakes). So if you 50/50 win rate, you will still climb a little if you are performing well as an individual (till you hit 3k).
So is there a need to point out others mistakes? You have no provided me an example where it has benefitted the overall playing experience of all involved.