Considering how bad his games originally were I'd probably agree with you, despite mediocre games from the get go he's still going. A huge component of his fame is due to mario and the console wars though. Let's face it smash bros brawl was probably the most exposure he had ever received.
And yes I'm aware that the viewpoint that the old sonic games were bad is not a common one. I also think that sonic adventure 2 is his best game so there's probably something wrong with me lol