I know this is a PR piece, but shouldn't a CTO know better? What could they possible not have achieved if they weren't using AWS? Literally every feature of AWS exists somewhere else. Maybe not all of the same features in the same place, but to say they couldn't run Stripe without AWS strikes me a bit silly.
Don't take it literally.
"I couldn't have made it to the top of the mountain without these specific hiking boots" doesn't mean it was literally impossible without that exact brand of hiking boots. It means they like the boots, it made the experience better for them, and they think the hiking boots are better than comparable ones.
I don't think the CTO is claiming that Stripe is solving a problem that would be impossible to solve without AWS. He's saying we wouldn't be as well positioned today if we had to solve the problems that AWS solves ourselves, or by relying on their not-quite-as-good competitors.
At AWS' scale, fully managed, when Stripe was founded (2010)? Bullshit. Back then, and even up until ~2013-2015 the state of the art was either VPS, colo where you DIY everything from the nuts and bolts to databases, Heroku/Google App Engine where you have little control, hosted VMware (utter shit), and slowly, AWS.
You're making the classic Dropbox mistake. Today yes, the majority of what you can do on AWS can be done elsewhere (mostly Azure and GCP, depending on specific features needed maybe one of the smaller ones like OCI).