This is wrong, because there are a couple special cases where we allow the user to edit member props even if the corresponding member prop def is read-only, namely:

// special case 1: property has a plugin-set error message - allow user to edit it even if it's a read-only prop,
// otherwise the user will have no way to give the property a new value and thereby get things to a valid state
// special case 2: required simple prop with no value - allow user to edit it even if it's a read-only prop,
// otherwise the user will have no way to give the property a new value and thereby get things to a valid state

So to implement this correctly, we would need to check whether each member map is read-only one by one, rather than just checking if the prop def is read-only.