The second-order effects that are described here around the "capture of upside" may be a little exaggerated. Credit cards and Stripe are common payment mechanisms for consumer, prosumer, and self-serve SAAS. I'm not denying there is a lot of money here, but I imagine the majority of B2B SaaS companies by revenue handle payment through annual contracts through checks and wire transfer.

I don't have any data here, but I'm thinking EHR, ERP, office building rent ("a SaaS company plus some glass and concrete") etc. If the service provided is annually worth 100k USD, theres probably human-human interaction which facilitates the exchange of legal documents and money. Think Oracle, SAP, ADP, ServiceNow, Workday etc.