"Execution is everything" is not tautological. It's not saying "execution is necessary" — it's saying that how you execute makes an order of magnitude greater difference than what idea you pick. Good execution will save all but the worst ideas, but an amazing idea will still fail if not executed well.
For example, Apple's Newton PDA: Great idea — it caught on like wildfire when Palm did the same thing a few years later. But it flopped when Apple did it, because Apple's execution was flawed.
But all you are saying is.
If you have an idea you have to try it out.
Yes obviously but try what out? What does it mean to execute.
And this is where it kind of falls apart from my point of view.
Saying "execution is everything" is as helpful as saying success is necessary to be successful. It becomes a tautology.
It's true but it's not really helpful unless you really think that just getting the idea is enough. But who here believes that?
What's great execution in one context is bad execution in another. Meaning that you have to execute to figure out whether you executed well.
You have to run the program so to speak.