The American constitution has a lot of good ideas. It also has a lot of terrible ones, and others that have aged poorly.
And that is going to be true of every Constitution ever written. A perfect Constitution is as likely as a perfect piece of software. In some fictional, never changing world, you could maybe imagine such a thing, but not in the real world.
The American constitution is a great first draft of a limited democratic government. There's good stuff there to build on. But it is sheer lunacy to think it's a done product that has all the answers to what we face today.