When it comes to stuff like this, where the lore can muddle things in regards to power levels, I look to popularity to settle the score. In that, Superman wins in a landslide.
Of course it wouldn't be an issue in the first place if they didn't live in the same reality, which they should not. Not saying ever power-level question can be answered with "put them on different worlds" (Superman and Wonder Woman for instance, that's always an argument and they very much belong in the same reality), but this one could be. Fawcett should be its own Earth.