Our core is also just huge, the outer core is larger than the moon and mercury.

I guess that could work? Earth is actually the densest planet in the solar system so our baseline mass > size ratio might actually be a bit abnormal.

Iirc near that +50% level you end up needing a saturn 5 to launch sputnik, so its more expensive to the degree that it might just be deamed unfeasable, at least at the technology level humans started launching rockets at.

The problem is you can’t have mountains like that on tectonically active planets (a mountain that big on earth would sink into the mantle), which is kind of a prequisite for a long-term magnetosphere so its unfortunately not something a species could likely ever have except as a result of terraforming a world like mars and setting up some kind of artificial magnetosphere.

I believe there is a generator with functional prototypes in the US and China that uses supercritical CO2? I mean its basically a steam engine but using a different medium and potentially even more efficient.

Even then all of them but solar are just spinning a wheel.