Hahaha! In fact class of medicines is called osmotic laxatives.
Osmolarity is certainly a thing but that’s why you have 2-3 liters of water in your hydration pack. Just as you were supposed to take old school gels with water you drink water after your super concentrated sugar water. Plus it might help your teeth stay in your head.
But I hear you on “what about osmolarity?” If you are taking in 100g of sugar + 1g of sodium, how much water do you need to make the solution isotonic? I don’t know but I bet it’s a lot. Thus my theory is that most of the time we’re using hypertonic solutions when pushing 100g/hr. Which can be a problem when it’s hot and the intensity is high!
Joe