Do kids these days not realize you can negotiate anything and everything with your vendors/suppliers/partners?
Yes, most SaaS companies LOVE it when you sign up for one of their standard plans, using THEIR standard T&C's, and standard payments.
But, DID YOU KNOW, if something is critical to your business, you can negotiate directly with pretty much every business on the face of the planet, and if your spend is large enough, or you're willing to pay, you can negotiate anything????
It's nuts, I know :)))))
Negotiating significant discounts needs a bit more work, commitment, or growth story. Discounts tend to scale with spend.
(Disclaimer, I now happen to work at Google, unrelated to cloud, but this was my experience at my previous employer)
Not sure if this has changed recently, but this was in about 2018/2019.
By all means use another payment provider as leverage to negotiate better contracts and rates, but I think it's unnecessary from a business reliability standpoint until you're very big and Stripe's downtime level (very small) is a material business risk. Spoiler: almost no one is this big.
My previous company had a business contract with GCP and so wouldn't be cut off for, for example, a dodgy employee account tied to the business in some way.
It's amazing how many people put their email and credit card in a form, pay sticker price for a service, and have their entire business depend on it. The terms of those contracts necessarily have to protect the service from all sorts of malicious users who just click sign-up. Talk to a person, get a contract, and the whole conversation changes (and yes GCP has account managers for this).