aha, I think we are coming at the term "walled garden" from opposite ends.
For a developer I agree with you, it is not a walled garden, they can sell games however they want, epic is one option who happen to be the only one that pays, out of all the stores, 3rd parties for exclusivity.
For a customer it is a walled garden for those exclusive games in that I cannot play those games without having to install and sign-up for the Epic Games Store because they paid to make them exclusive (again, permanently or temporarily).
For a developer I agree with you, it is not a walled garden, they can sell games however they want, epic is one option who happen to be the only one that pays, out of all the stores, 3rd parties for exclusivity.
For a customer it is a walled garden for those exclusive games in that I cannot play those games without having to install and sign-up for the Epic Games Store because they paid to make them exclusive (again, permanently or temporarily).