"Just build it from scratch, can't be that hard" - every software engineer at some point in the past.

It is that hard and even harder. An then you have the problem that politicians and societies have a hard time to decide on topics of much narrower scope and much smaller impact.

That said, I would love to for the US having a solid checks and balances system instead of the current system.

If you want to look at a case study regarding a 'more modern' constitution: the German (de facto) constitution is only around 80 years old.

Interestingly, both the US and German constitution were written explicitly to limit the power of the federal level. But in both systems the federal level grabbed more and more power as time went on. (Partially because that's also popular with the voters.)