OP, your entire post is attempting to deflect the responsibility that was yours.

How could you conclude that it is anyone's fault other than your own?

The point of detention is intended to be a punishment for your actions. You were held in immigration detention for 6 hours. You should be grateful it wasn't overnight.

It's curious you omit your country of citizenship in you post.

I dare say you won't travel to a country without ensuring you have a correct visa in future.

Ironically, had you been denied boarding I suspect that would be another rant on FT about the airline not notifying you earlier.