Dutch's team had extensive jungle warfare experience. Especially Dutch and Billy.
This includes things like moving silently, reading maps and knowing your way around, making traps, getting food and water, etc.
Perhaps it didn't make a big difference because the Predator was so overpowered, but a Colonial Marine wouldn't have been able to fight like Dutch did in the end.
I would just image the Colonial Marines stumbling around like idiots and getting killed in a prolonged fight.