There is a big difference between a realm-wide policy/law of "no other religions", and "it's the lord's decision". While the end result may be the same in many, the second is much easier for outside religions to penetrate. Also, the policy of "it's the lord's decision" makes the realm's policy *the exact same* as nearly every other realm on the island. And unless you were to poll every lord in every realm, you can't know whether any realm would collectively allow/forbid any individual religion. Any less is just uninformed opinion or blatant propaganda. And you never know, the results may surprise you.
