(even after adjusting for the incredible injustice of all the external actors, and nature itself).
If you are lucky enough to get such a stable system, it's a high priority to defend it. Don't weaken it for marginal improvements for your cause.
Turkey is much more stable than Haiti, but Erdogan managed to build an authoritarian system centered around him anyway, and a constitutional change towards presidential system was a crucial step.
Presidential system might work in France and the US, but especially in the US the near future of it is still uncertain. Trying it in countries that barely hold together doesn't seem wise.
France has a semipresidential system, not a presidential system - it has both a President directly elected by the voters, and a Prime Minister accountable to the legislature, with the two having a (somewhat complicated and uneasy) division of powers - essentially, the President controls foreign relations and the military, the Prime Minister controls most domestic policies. It works reasonably well when both President and Prime Minister are from the same party, it works with more acrimony when they are from opposed parties (cohabitation), the recent political upheavals in France have led more and more to question if it is still the right system, or whether France should return to the parliamentary system of its Third and Fourth republics - but, even at its worst, I think it still works better than the presidential system used by the US and much of Latin America. The presidential system concentrates too much power in a single individual, who is difficult to hold accountable, leading to the problem of strongmen (caudillos) which have been a plague upon Latin American history-and maybe now with Trump the US is starting to move in the same direction
So your point about whether "you are lucky enough to get such a stable system" is inaccurate. It's not luck. People created those systems. You can even see how that processed happened, deliberately, in recent history in places like Singapore.
The first half of Behind The Bastard's episode on Baby Doc has a pretty good summary: https://www.youtube.com/watch?v=qTEEokXizd8
Sure, the people have an outsized influence on the success of a nation, but the institutions also shape the people and empower some people over others. Can you imagine how much differently the US would look if it wasn’t founded on slavery and oppression? If women didnt have to wait 150 years to vote? If we didn’t institutionalize a gerrymanderable legislative system?
The institutions matter AND people matter, but bad institutions empower terrible people.
Where is there evidence of this?
I don’t think that is really fair on France - many of those failures were due to defeats in war - for example, the Third Republic didn’t “fail”, it was conquered by Nazi Germany - and when it was liberated, the French decided to take the opportunity to rewrite their constitution, but I think that was a choice rather than something they were forced into.
And the Fifth Republic was engineered by de Gaulle given the opportunity of the 1958 coup attempt. If de Gaulle had unexpectedly died of a heart attack in 1957, the Fourth Republic might have survived. Probably the 1958 coup attempt would still have occurred even absent de Gaulle - but neither its success nor failure would have necessitated a rewrite of the constitution (as opposed to maybe just some tweaks), although certainly it could have resulted in one. Even de Gaulle didn’t have to rewrite the constitution, he decided he wanted to and was handed the opportunity to get what he wanted, but maybe in some alternative timeline he didn’t feel as strongly about that and so the constitutional rewrite never happened
Why didn’t the American Civil War result in a rewrite of the US constitution? Probably because the Union had a clear and convincing victory. If the Union had lost, or if the war had turned into a stalemate, much greater odds the US constitution would not have survived it - a less-defeated Confederacy might have negotiated reintegration into the Union subject to a constitutional rewrite; if the Confederacy had won and retained its independence, the Union might well have decided to write a new constitution in response.
The US constitutional system has arguably been reconstituted at least 3 times (in order of plausibility): US Civil War and Reconstruction amendments, FDR and New Deal, LBJ and Civil Rights Act of 1964. The latter two were not even primarily accomplished via formal Constitutional amendment, just a reinterpretation of what the Constitution allowed and compelled. What makes Trump different than those? Just the fact that, unlike the first three, it's more right-wing than progressive?
I’m not saying that whatever is happening now is necessarily good, but will it lead to the collapse of the US Constitution?
You need the benevolent dictator, then the stability, then the slow introduction of government by the people over decades.