That's an interesting thought and I like where you're going with it, but I don't agree that the Revolution was a proxy war. The American campaigns of the French and Indian War, or Seven Years War, I'd argue is a better example of a proxy war as France and England battled through colonists and native allies. The irony is that British colonists in North America were appalled at the casualties their militias sustained during the early-mid 18th century and demanded a Regular Army presence; this same presence, and the subsequent taxation to fund it, would eventually be cited as justification for the revolution.

When discussing proxy war, I think of Soviet involvement in Vietnam or American involvement in the Soviet-Afghan War as examples: one power wages war against another through a third party that they supply materiel and aid to without becoming involved in a martial capacity. The Spanish actively engaged the British in the area around Florida during the Revolution, and the French Navy regularly engaged the British forces. If you look at the Siege of Yorktown, French forces made up almost half of the total force! These men were not there in an advisory or logistic/support role, they were combatants that were engaged against the British forces.

The British paid for mercenaries throughout the course of the conflict to bolster their forces. Hessian and native troops made up, at times, a very significant portion of the British military presence. I'm sure that at times there were at least skirmishes between non-British and non-American forces, however overall the war was not by proxy.