The only Hessians who were mercenaries were the ones who defected and fought for the Colonials.
Believe what you want but there is a small line in the Declaration which contradicts you:
“He is at this time transporting large Armies of foreign Mercenaries to compleat the works of death, desolation, and tyranny, already begun with circumstances of Cruelty & Perfidy scarcely paralleled in the most barbarous ages, and totally unworthy the Head of a civilized nation”
Maybe you could expand on your version of reality so that we can see where the Founders and historians like Lowell went wrong.