So harder to regulate your temperature then? Not sure how that's an advantage.
Less body mass will cool down more quickly, in very hot conditions, or not get quite as hot in the first place. Being a 'skinny' bod, I don't suffer nearly as much as tubbies, in the summer.
No point in arguing this one. Top athletes tend not to carry around any excess flab. There are very good reasons.
It's quite simple: Excess fat = lower bodily efficiency. Fact. Medically, scientifically, proven FACT.