Personally, I prefer soft locked weapons like the Shadow Dragon´s Excalibur. It has the exclusivity of personals and flexibility powered by lore. Having a strong weapon so early gives Merric a nice advantage in the field and tell us that he has something special, in this case, being pure hearted and the student of Wendel, who is also capable of handling the Excalibur due to his experitise with magic. Having a weapon like this, who can chose its wielder, sets a presedent of personal improvement for its wielder, like Ellerean, who at base, can´t use the Excalibur, lorewise because of its lack of compassion but after learning his lesson and honing his skills with magic, becomes worthy, gameplaywise, reching weapon level B.
Now, for class exclusive I feel that weapons ranks and the kind of weapon the class uses serves as a better way of doing exclusivity than letting only a few characters in your army to use them. If anything, they should have soft locks like Excalibur´s, there´s nothing in particular to a lord to make it being able to use a rapier, special if we consider that a class called SWORD MASTER is not able to use one kind of sword (to be fair, it is a dumb name, is more like a title like General than the way you would call a unit; fortress knight makes more sense).
Nosferatu is a wierd case because it has changed a lot throughout the series. However the 3DS ones seems more like a remnant of a different weapon class who is now mixed with the other two than an actual asset of a class. Maybe IS could´ve work a magic tringle with the new Spirts from Hoshido replacing light, anima just as usual based on elements, nosferatu being one of the darks. That way, the norian magic users would be differentiated by using dark magic and the hoshidians spirits, anima is fair game for both but I guess they didn´t wanted to have a slot in the triangle with only one representative and gauntlets weren´t invented yet.