The vast majority of merchandise and food service locations don’t use a computer system that will display the type of ticket a MagicBand is linked to, and the ones that do mostly don’t have access to guest demographic information that would allow them to validate ownership of that pass. Disney uses at least four different internal computer systems that I’m personally aware of, and I’m sure there are others. Most of them don’t talk to one another in any meaningful way.
I’d personally like to see a “digital membership card” in the MDX app, the same way that DVC members can access a digital card via their member services website. (I’d also like that card to be in the app, while we’re at it...) This way people could show the digital card plus an ID for discounts just like DVC. Some CMs already allow guests to show their pass via the app anyway - it’s not official policy, but it would be an easy modification to the app to do this for real.
Also, since the FL Resident Monthly Payment Plan contract was mentioned - nothing in that contract guarantees a guest’s right to any discount. That contract exists to protect the company, not the guest, if you read the language in it.