OfflinePuffin I think the problem here is not that GrapheneOS users don't trust GooglePay to handle their cards and would trust another company, but rather, GooglePay doesn't trust GrapheneOS so limits the functionality of GooglePay by not allowing contactless payment nor adding of payment cards in the app. Hence, if you want to use both GrapheneOS and contactless payment, then your only option is to use a third party app that does trust GrapheneOS (or figure out a way to hack the source code so that GooglePay will trust GrapheneOS).
But it's a good question to ask, whether Curve is actually trustworthy. I'm hoping yes. If anyone has experience or information that can help shed light on this, please chime in.