Having a president or a prime minister type position isn't inherently a bad idea. It's useful for diplomacy and in a genuine emergency when there isn't time to waste waiting for a committee or a council to reach agreements having one person coordinating the response is far more efficient.
The problems start when one person is imbued with unnecessary, overbroad, perpetual, unaccountable powers. In such a system the person wielding those powers will inevitably be found to be compromised, or corrupt, or simply inept and easily manipulated.
What 'Murica has though is so much worse.
We have an empty highest office; a charade of power and responsibility. The job title of "president" (but arguably one could also include "senator", etc. as well) is merely a focal point for citizens' demands and complaints, anger and accusations. The actual planning and decision making is done by permanent state operatives for reasons and goals that nobody has explicitly condoned via the ballot box. For the most part these reasons and goals are never publicized or acknowledged at all.
We have only the illusion of a representative government and the funniest part, to me anyway, is that it's the people who aren't being represented who maintain and reinforce the illusion. I guess it's less painful than admitting one has been a dupe sired by dupes who were sired by dupes.
Self-delusion is a fine 'Murican tradition.