My kiddo is 18months old today. He’s 27-28lbs but he wears size 6. They fit him better and hold more. The diaper “weight” ranges really depend on the kid’s shape and the diaper’s fit. Kids who are too young for potty training can absolutely be wearing size 6.

Size 6 and size 7 diapers have been a huge life saver to me. And not because my kid trained late- he self started right at 2 and is trained now at 28 months….
But he hit 35 lbs at 18 months
He hit 42 ish at 2.
Some kids are bigger.
Your “theres that” line is fairly shamming to bigger children.