(Tl;dr - good for Britain, good for the world, less clear for the US.)

This is a fun question. I’m coming at this from a largely British perspective and trying to work out what the counterfactuals are for Britain and America. Obviously an awful lot of this is extremely speculative so take it my attempt at a fun thought experiment.

For Britain narrowly, I think the American Revolution has to be seen as a good thing. It was a striking assertion of British liberalism in practice that must have in some way emboldened domestic British liberals to push through the political reforms of the 19th century - as well as acting as a beacon of Enlightenment liberalism globally. It probably encouraged the decline of mercantilism in Britain - would the repeal of the Corn Laws have happened if the American colonies remained within the British Empire? What would the lack of a free-trade Britain in the 19th century mean for the status of free traders in global politics today?

It likely also sped up abolitionism in Britain. Britain in 1776 was clearly well on the road to becoming an anti-slavery nation - e.g. the Somerset vs Stewart case of 1772 had already established that slavery was illegal under English law (similar rulings came through from Scottish courts very soon afterwards) and any black slave setting foot in England would become a free person. But it took over three decades for this to translate into the abolition and suppression of the Transatlantic slave trade in 1807 and another generation until the freeing of all slaves in the Caribbean colonies in 1833 - largely because of colonial and slave-owning interests. If the pro-slavery American colonies had remained British through that period, that would meant more loud voices against abolition that would have delayed 1807, delayed the creation of the Royal Navy’s West Africa Squadron and maybe meant many more innocent West Africans kidnapped and transplanted to slavery in the Americas.

For the US, if the American Revolution hadn’t happened I imagine many of the outcomes (a self-governing democratic English-speaking nation) would still have come about in the 19th century as they did for Canada, Newfoundland, Australia, NZ, etc. But that means that happening at a different pace. The US would probably operate a parliamentary system like the other dominions, which I think is a better system that is less open to executive abuses - the likelihood and impact of a Trump administration today would probably be lower in a parliamentary US.

The flip side of no American Revolution meaning a slower pace of abolition for Britain would be a faster pace for the US: Britain was one of the earlier abolitionist countries, the US was one of laggards, so in this alternate scenario I imagine they’d both end up somewhere in the middle.

Then harder to assess is the question of the loss of the symbolic status of the American Revolution in the liberal world.

But overall - I’d find it hard to disagree with the idea that for Britain and the wider world the American Revolution was a very good thing; but I can see a line of argument saying that, on slavery and on the type of democracy the US would eventually become, going down the route of Canada and the dominions might have led to a better outcome?

TLDR, the Revolution was probably inevitable, and while the nation’s founding fathers had their hearts in the right place with their ideals, they had some cognitive dissonance and slapped together a very flawed system.

On the revolution itself, I think it was probably inevitable. The Seven Years War/French & Indian War exacerbated some preexisting faults between the 13 American Colonies and the British Parliament. While I do think there is probably some post-revolution revisionism surrounding the American Revolution, it only happened because there was sufficient desire to leave the British Empire.

As for its founding fathers and their ideals I think their hearts were in the right place, but they did not properly follow through. While the US is generally moving towards a “More perfect Union” there was definitely cognitive dissonance between the founding fathers and their own ideals; how Jefferson could genuinely write:

“We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.”

while himself owning slaves is only possible if there was some serious cognitive dissonance.

On the whole, they managed to slap together a government that has lasted 235 years (at the time of writing). That, I think, is pretty good considering the 13 colonies were a shit show of competing, conflicting ideas and visions for what the US should be. Indeed, some were even under the impression that it would be 13 separate countries. Consequently, the government they put together is extremely flawed. While some of these flaws can be explained away as them trying to navigate the issues of the time and get the 13 colonies to simply agree to a union, the simple reality is the consequences of their compromises are being felt today. Slavery, of course, was the nation’s “Original Sin” and biggest fault line, requiring a Civil War to finally end it. Even then, however, the lasting effects of slavery still haunt the nation and were never adequately addressed.

As for the rest of the flaws, they all boil down to having too much emphasis on the individual states and not enough emphasis on individual voting and equal representation of citizens between states. (In my opinion, this is ironic because the lack of representation was explicitly stated as a cause of the Revolutionary War, and then they created a new system wrought with unequal representation). It is understandable how this came to be - at the time, a system based on population alone would have been dominated by Virginia - but that does not change the fact it is damaging and improper in our contemporary context.

The solution to these problems is outside my area of expertise, but on a surface level I would propose at least the following structural changes:

1. Abolish the electoral college. It is outdated and dilutes the principle of equal representation (1 citizen = 1 vote, always)

2. Repeal/amend the Reapportionment Act of 1929 which resulted in citizens of large states losing some representation in the House of Representatives. (Additionally, they are already knee-capped by the electoral college and the Senate).

3. The Senate. I do not know what we should do about the Senate. By design, 2 senators from each state is a violation of the principle of equal representation of citizens between states. That aside, they are usually the more rational and civil of the two chambers of the legislative branch. However, the fact that states like Wyoming, with a population of 576,000, has the same voting power as California (39 million), or Texas (32 million), or Florida (23 million) or New York (19 million) is very questionable. There are many more small states with a very low population that have outsized influence over the nation because of the Senate. This is true when one takes into account population sizes, but also economic output.

Edit: Spelling

The American Revolution had a lower impact on the modern era than the Civil War did.

It’s not really possible to gauge the impact of the Revolutionary War because it got overshadowed by the Civil War.

I think we should revisit the causes because I feel we’re approaching another one.