Source on type 2 being mostly genetic? All I've found is there is some link but not conclusive.

Also T2 is on the rise in young people. Have their genetics changed dramatically in the past few decades? Or has food?

https://www.cdc.gov/diabetes/data-research/research/young-pe...

This is a simplification. Type 2 diabetes is heavily polygenic, but the genetic connection could be... you are genetically predisposed to like sweet food! In which case, the diet intervention would work, most people just aren't willing to do it.

Many genetic predispositions are behavioral, it's not all pure metabolic effects.

lol no