[buro9]

This assumes the incentive is balanced for the vendor, that they'll win as much business (or more) than they'll lose.

I don't believe this is true anywhere, but specifically those vendors who are most aggressive about creating walled gardens and who have high revenues with unhappy customers looking to leave are both the sweetest spot for your end user demand and vendor resistance.

I suspect that you hope to leave those vendors (when discovered) until later, once you have momentum. But I also suspect that these will be the ones end users demand very early on and that end user perception of usefulness of your service is linked to the difficult vendors.

Additionally you have a time and opportunity window problem. Changing vendors isn't core to the business of most companies, and instead it's usually the product of a concern at a point in time (i.e. costs this year) that comes with limited window in which to execute on the project (i.e. we'll only distract ourselves from our core business for the next 6 months to try and reduce costs, then it's back to core business). This is going to make end user acquisition harder (more expensive) for you than most startups as you're going to have to invest more in the marketing to ensure you're on their radar at that point in time (with the assumption you can execute within the window of opportunity).

I'm not down on your business, like others in this thread this is a thing I've touched at the peripherary of my career and I'm just sharing my thoughts. You've picked a hard problem and if solved it definitely has value.

[SamuelAdams]

Honestly if I were OP I would specialize in a certain industry, ie healthcare, manufacturing, apparel, auto, or similar. Then get familiar with the big software systems all these people use. Systems like Epic and ERP systems in general take companies hundreds of millions of dollars to migrate from and to. If their company can automate even a little bit of this, that would be very lucrative.