And besides which, the H-4 was a one-off prototype that made one mile long flight at an altitude of just 20m. It's not clear if it would operate well higher up where there was no ground effect
Some of the Ekranoplan ground effect vehicles can fly that high and they are probably larger. Not exactly aircraft though.
I'm 90% convinced that the spruce goose was mostly war profiteering like a few other useless things at the time that we like to forget. Hughes was a "sharp businessman" after all.