Azure AD is the biggest in the game by far in terms of SSO, stretching every vertical from education to investment banking.

Azure AD B2C for customer IAM is lagging way behind Okta/Auth0 etc. Sure AAD is great enterprise users or B2B but millions of customer login, branding, app experience B2C sucks.

...only because of Office 365 though.

If Cognito is the AWS offering you're talking about then it doesn't even begin to compete. It's really a terrible product and AWS has misled us about the roadmap multiple times specifically in relation to multi-region support.

When AWS Cognito had it's outage in November, I was quite happy we went with Okta.

I'm unimpressed with it as well, but I suspect antitrust officials have a different definition of "competition" than we do.