My question is about the spin of the neutrino, and the evidence (or speculative arguing) for its magnitude which is not proportionate to its mass.
You are dealing with "things" that are supposed to be point particles, so they should not, in classical terms, have a mass in the first place. The math takes over from common sense notions on this scale, and the spin of the neutrino has to be 1/2 to conserve quantum numbers. The mass is the link between the classical world, in which we expect it to be a certain value, and the quantum world, in which the particles are not real in a way we understand.
I hopefully will not annoy you because you already know this. Because "spin" is an analogy, with absolutely nothing to do with ordinary soccer ball type spin, you could have asked the same question about the top quark, which has a huge mass but still has spin angular momentum of 1/2, because that is what we define it to have.
So comparing the mass of one point object (which classically should not have a mass) with another point object with lower mass, and expecting a different angular momentum will not make sense in ordinary terms, but this is not the ordinary world you are asking about.