I can confirm that this statement is absolutely horseshit :)
Evidence: I play on a soup kitpvp where I'm one of the better players. And I'm a Silver in soup on Badlion. The level of toxicity is far higher from new/unskilled players than the regulars. However, there's probably a bit of truth in what you said, in that people that are unskilled aren't people who have spent hours of their lives improving on minecraft pvp and getting frustrated on losing. They just play the game for fun, not competition (or they find fun in the bit of competitiveness involved)