Since when does checkout needs to be an "experience"?
I'd much rather trust Paypal than a company worried about losing track of me or that I might see a different branding.
That different branding is the very reason I'm doing the transaction in the first place: I trust Paypal way more than any company's self-hosted checkout.
Checkout has been an experience for decades. The candy/magazines by the checkout line in your grocery store are now ads on the cart page. Amazon even promotes using a specific credit card in some cases: Use Discover to save 5%, or Save 10% when you get an Amazon Visa.
I'd much rather trust Paypal than a company worried about losing track of me or that I might see a different branding.
That different branding is the very reason I'm doing the transaction in the first place: I trust Paypal way more than any company's self-hosted checkout.