Ah, but core temperature isn't what we're interested in here. We're interested in the surface temperature. What are the dynamics of a star's atmosphere - of the outer layers of gas not participating in nuclear fusion? Well, there's gas pressure which tends to make the atmosphere expand and cool, and gravity which tends to make the atmosphere contract and heat up. As the atmosphere expands and cools, gas pressure decreases, and as the atmosphere contracts and warms, thermal pressure increases, and eventually an equilibrium is struck where the gas pressure outwards equals the gravitational force inwards.
The core heat source is actually secondary to this. More massive stars are hotter because they are more massive - the sheer mass of gas that collapsed from a nebula to form such a star provides huge amounts of energy by gravitational accretion. Then, because of being so hot to begin with, they burn fuel faster than their smaller, cooler cousins, and that keeps them hot.
So the largest stars are the ones where the equilibrium is found at a point where the atmosphere is large, sparse and cool, and hence red. This isn't such a star. In a super-hot star like this the radiation pressure comes to predominate over gas pressure, and that has a tendency to blow any surrounding gas clean away. It's too heavy, and, as you say, too hot, and very unstable. So it can't form a well-behaved convective envelope around itself and become a red hypergiant. It remains a very massive, very hot, and very luminous star, but it never troubles the list of the largest stars known.