There could certainly be a way to provide Edge via the Store and not force it on users. Possibly the reason it's not done that way is because there appears to be hard links to it. Despite setting Firefox as the default things still open in Edge, like from the Search in the Start Menu and from Settings help pages etc. Maybe there's a way to fix this but it feels wrong to me. And it also doesn't need to keep pinning itself to the task bar either.