Cool....Shepard is saving the world. Good for him. And as I said, many people want to experience something in the MEU other than 'saving the world'. There's important events in every person's life. Shepard doesn't negate that.
Sure, 500 years into the future you could be fighting the same pirates 'you' speak of. However, they (Bioware) would either have to canonize an ending or trivialize all of them. There's no way to say they (the endings) didn't happen or 'dont matter' anymore.
And yet you're wrong again. All three endings are "crucial" changes. Yup, AI's will come back after Destroy, and then they may even wipe out all life in the galaxy (forever) due to the Reapers absence. Control is crucial because it changes the entire role of the Reapers from galactic harvesters to galactic guardians (and they will surely be around in 500 years). And Synthesis basically makes all life in the galaxy unified at a new origin point in order to include synthetics.