I might agree with you. I feel like many of the better American Porters (as least what I like) are right on that Porter/Stout line. I have been working on an American Porter recipe mostly as a challenge to make one that would do well in competitions.I thought Founder's was great, but stout is pretty nearly the same thing, and I like it much better, so I don't see any point in trying to make porter.
I do really like a more robust version of an English Porter though. Something that is in the 5% range with flavors from EKG Hops, Marris Otter, Brown Malt, Chocolate Malt, Black Malt, and English Crystal Malts. I find these beers to be really refreshing any day of the year with a feeling of sustenance to keep me going while working in the garden on a hot summer day.
That is the beauty of homebrewing. You get to make what you like to drink and call it what you want to call it!