You seem to be doing this in good faith but honestly, there is no difference between 'Discovery Call" and a "Sales Call". The point is that the customer has to speak with someone first. I do think it is required for enterprise deals but the premise of your post seems to say otherwise.
The call offered here is optional isn't it? You can engage entirely over email for enterprise deals.
Yeah, I was annoyed at this too but I think they're differentiating it by having the price already set, and it's just a way for Companies to do the intro dance if they want to. I know my immediate decision-makers at my company wouldn't use a vendor if there was no call.
There absolutely is a difference between one 15-minute call to see faces vs a pipeline of ten 30- to 60-minute calls discussing requirements, compliance, pricing, billing, onboarding, implementation, and support over the course of 6 months.