Reading 5w-30, it's the last number (30) that indicated the thickness of the oil at operational temperatures. When I mention 30 weight I'm talking about 0w-30 or 5w-30 or 10w-30.
5w-30 (Resource Conserving) oil after it shears isn't that much thicker than 20 weight oil. Resource conserving oils are usually on the thin side of 30 weight (cSt in the 10s) to start with and they shear (HTHS 3.1<) because of the friction modifiers put in them. American cars are built to meet CAFE mpg standards.
Motor Oil Viscosity Grades Explained in Layman's Terms
30 weight motor (Not Resource Conserving) oil for European cars is thicker and doesn't shear as much (HTHS 3.5>). If someone is having an oil consumption problem and wants to step up in thickness then German Castor 0w-30, Motul, etc...
I wouldn't worry that your dealer used the right oil. He probably did, and if not 5w-30 (Resource Conserving) is okay. You won't notice a difference on mpg. Most of your friction is in the form of wind resistance.
Subaru backed away from the 7,500 mile oil changes for 2015. The new guidance is 6,000 miles. I don't know why they did this, but I'd change my oil at no more than 6,000 miles. I'm debating 5,000 mile oil change intervals myself. Once my car has some miles on it, I'll send the oil in to Blackstone for analysis. Then I'll decide...
Check your oil level at least every other fill-up with gas. Having oil is most important. LOL