Amazon, Walmart, Target and then increasingly unsure.
But they have partnered with GS and MC. Far from any sort of "finance industry roots".
They essentially offer a fancy UI on top of GS products and other traditional banks.
Apple Cash -> Green Dot or some other no name bank
Apple Card -> Goldman Sachs
Apple Pay -> some very small percentage of the bank and network fees charged to merchants
In some countries the vast majority of payments are done via phone apps for national payment systems already, bypassing Visa/Mastercard etc. entirely. Even kids pay for candy by phone.
> Likely Apple currently has the deepest finance industry roots.
Apple used a very large bank headquartered in the US for its credit card processing as of about ten years ago. Given that the cost of change is significant once these processes are put in place, it is likely this remains the case.
Note that this is not the same as what Apple Pay supports.