ok so i am correct, you can kill the final boss with only the air die maxed out, but you have to be frickin lucky
no idea but you would need to deal 600 damage in 20 seconds
at max upgrades, the cooldown is 1 second and you get 5 air dice with 4-7 damage each
that means the absolute minimum you can do to the final boss is 400 damage (20*5*4)
to kill him, at minimum, you need to get all 6s or any combinations of 7s and 5s that adds up to 600
i was going to do a bunch of math to figure out the chances but i realized it's more complicated than i initially thought, so my answer: very lucky.