What "decisions so outrageously and implausibly stupid" are you referring to?
Almost all of them? But specifically that it would be a jolly clever idea to a) attack across a narrow field, waterlogged by recent heavy rain, which had also been ploughed recently and that was hemmed in by woodland on both sides, b) to dump all the various lighter supporting elements of the army behind the main offensive battles* without any real idea of what to do with them, c) to just blindly throw everything forward across sad astonishingly muddy field in a mad rush.
The thing is, by 1415 French armies had a substantial structural advantage over English ones: after disasters like Crécy it was understood that it was not a very good idea to launch massive charges of mounted Knights against supported longbowmen, and so the tendency was for the bulk of the Knights to fight as dismounted Men-at-Arms instead. Massed archery was very effective against cavalry, but was not so useful against heavy infantry. Something like Agincourt should have been completely impossible, which is the main reason why it swiftly became such an iconic battle.
*Divisions of a late Mediaeval army.
