I am pretty sure the reason that Magus saw the sword being more powerful was because it was reforged with more dreamstone.
Now about that Non-Legend malarky
[Young Woman] Only the ancient sword, «Masamune,» can defeat him. And only the Hero can wield it!
[Young Man] Did you know? They say the mythical Masamune lies deep within the Denadoro mountains. But it's guarded by terrible beasts.
Frog: The legendary Masamune is required to fight Magus. And I've no right to wield it.
So it says the Masamune is legendary, but it doesn't say a specific legend about it. Hmm.
True, the Masamune was old, but Cyrus was able to beat Masa & Mune to get the sword, so it's safe to say he was a good swordsman. I don't think that the fight between Cyrus and Glenn vs. Magus and Ozzie would have been a pushover for Magus and Ozzie. Which would mean that Cyrus would have hit Magus with the Masamune at least once before it broke. If Magus was affected by the Masamune just because it was made of Dreamstone, then he would've known it could do that already. Instead, after defeating him in his castle, he is suprised. The sword was made of Dreamstone before it broke and after it was fixed. That is why Frog is the reason the Masamune worked so well on Magus.
Now, for the case of the Mammon Machine, I think that the Masamune absorbing it's energy
is an innate ability of the Dreamstone. Think of it like this: You take two car batteries, one fully charged and one much less charged. You hook them up to each other and the fully charged one will, over time, lose power to the less charged one, until they both contain the same amount of energy. I think this is a great comparison, since both the Masamune and the Mammon Machine are made of Dreamstone. It's a simple case of equilibrium. Magus is obviously not made of Dreamstone, hence, the Masamune drains his energy for a completely different reason, which I stated a few posts ago.
