Are they? What did Facebook disrupt? What did Highrise disrupt? What did google disrupt (in search)? Some technologies are disruptive, some aren't. Many are just a little bit better and that snowballs into a large advantage over time, especially in winner take all markets. Just because a company is huge doesn't mean it's disruptive.

Walmart started as one store, don't believe you can't compete with them, I see mom and pop shops sell products in the same categories as Walmart and win.