"Also the absence of anything that looked AT ALL like a bell curve distribution of ability. The battle school kids are all supposed to be massively well selected and trained, yet only Ender, Bean, Valentine and Peter really matter. "

If you select out the right end of the bell curve from the general population, then you won't have a bell curve anymore, but rather a fat lower end.

Also, the training was supposed to be a sort of abstract sport to select for leadership skill, coolness under pressure, etc - it wasn't supposed to be actually training them to fight in space. They did training of the actual spaceshippy stuff later. You could certainly argue they should have started that earlier though.