Today the cloud market has many players. Yet if Amazon’s entire public cloud were a single computer, it would have five times more capacity than those of its next biggest 14 competitors—including Google—combined. Every day, one-third of people who use the internet visit a site or use a service running on Amazon’s cloud. (Netflix runs on it almost entirely.) That’s one reason why, when a portion of Amazon’s cloud goes down, it can seem like the entire internet has failed.
So yeah, AWS is huge. Google and Microsoft will have to battle over ever decreasing margins (which Amazon historically never seems to care about), sticky API's, and an absolutely overwhelming head start.