You know you can just use regular cryptography to validate data, right?

Also, you always have to trust someone, in this case Stripe.

Regarding L1 blockchains, how exactly do they solve the speed problem for a distributed global database that needs to be replicated everywhere for the security guarantees to actually work?

What do they forgo out of https://en.m.wikipedia.org/wiki/CAP_theorem ?

Pretty much always A. In systems like this, it's better to deny transactions than allow inconsistencies.

non-potatoe hardware and elbow grease in the software https://github.com/anza-xyz/agave