Dylan Matthews, a clever and provocative writer at Vox, has a holiday weekend piece arguing that the American revolution was a mistake. He offers 3 reasons: slavery would have ended earlier; the natives would have been better treated; and we would have a parliamentary government, which he says is more decisive and less prone to dictatorship than presidential systems.
He's probably right on his first two reasons, but I'd note that many parliamentary systems have failed pretty badly: several of France's Republics; prewar Japan; Italy on several occasions; and, of course, Germany on two disastrous occasions.
The independent United States also made positive contributions to world history: leading the way in democratic governance and an expanded suffrage; building an economic powerhouse; using its strength against tyranny and to create a liberal world order. What Matthews doesn't speculate on, but which would tip the balance for or against his argument, is how the trans-Mississippi west would have developed. A French empire? A Spanish one? A restive border region where native and European forces came to blows?
It's fun to ponder alternative histories. But Matthews has a weak case for labeling independence a mistake.