The problem isn't necessarily who has the power or how many people are in control of it (the President isn't a monarch, and congress holds most of the power generally). The larger problem is the size of the power and the weakness of the current checks against it.
The way the system works today politicians bribe the public with their own tax dollars and in so doing get to hold onto power and the perks thereof. But even if we make it more direct the problem of people funneling the government trough into their own mouths, to the detriment of society, will still exist and, if anything, be even worse. And that's aside from the explosion of bureaucracy and regulation which has happened and continues to happen which is also a big part of the mess we're in.
Edit: Also I should mention that a lot of the aspects of the system works today which seem like defects (gridlock, slowness, etc.) are there by design. The system is designed so that gridlock is typical and to have a lot of friction on big changes. That ensures that the power of the government isn't subject to random vicissitudes, fads, or slight changes in the balance of power. It takes consistent majorities in public opinion over periods of time to translate into action, or very large majorities to translate into action quickly.