hey just a wild theory:
what if madara reason to send the kyuubi to konoha was not to crush konoha?!?
well this is a wild assumption, but what if danzou is madara twin brother, as he lost his eyes, he could had get new ones from someone normal eyes, he doesn't have the power to perform the time-space jutsu that's why he is old, and maybe weaker than madara.
and the main reason for madara to send the kyuubi to konoha was to crush his brother, cause he want to be the strongest. Minato understood that and took madara's key (kyuubi) and entrusted it to the only person he thought that would be able to stop this c?chaos, to is own child