LOL. Ridiculous. First, they hadn't "just" freed themselves from British rule. The war was over in 1783. The colonies continued under their existing government until 1789, when the Constitution having been ratified, was put into action.
Second, their charter did anything BUT "carefully define" powers. "Necessary and proper" clause? "general welfare" clause?
Third, separation of powers was NOT a novel idea. The states had republican governments, with an executive and a legislative branch. They had a judiciary. The only thing novel was the pretense that federalism was something other than nationalism--that the states would be anything more than mere counties under the new system.
The purpose of the Constitution was to enlarge the central government, to make it a complete, consolidated government, and to make sure it had dominion over the states.
But hey, if you like fairy tales, then just ignore me.
“just ignore me”
That is the intelligent portion of your post.