If you have a maximiser of A, the ability to constrain that maximiser, and the ability to generate A, you can use it to maximise B by rewarding the production of B with A. If A = entropy and B = utility, Q.E.D.

That seems to simply be buck-passing. What does this gain us over simply maximizing B? If we can compute how to maximize a predicate like A, then what stops us from maximizing B directly?

You said you didn't see how having an entropy maximizer would help with maximizing utility. Having an entropy maximizer would help a lot. Basically maximizers are very useful things - almost irrespective of what they maximize.

If you know go, that's pretty similar to winning.

Pretty similar, yet somehow, crucially, not the same thing. [...]

Sure. I never claimed they were the same thing.

If you forbid passing, forbid suicide and aim to mimimize your opponent's possible moves, that would make a lot more sense - as a short description of a go-playing strategy.