They were quite champions today.
That version is not used but perhaps not for the reason you think.
Let us start with the singular.
He was quite a champion today.
That is possible but not the usual idiom. We are more likely to say:
He was quite the champion today."
I have no idea why.
Pluralise that and you get:
They were quite the champions today.
...and that is idiomatic.
P.S. I see that this is currently being discussed in the comments. When we say "'You are quite the champion" it actually means "You are are quite a champion." Again, I don't know why. Maybe someone else has an explanation.
We should not be led astray by the fact that the word happens to be 'champion'. You could perhaps object by saying, "Well there can be only one champion". In fact the idiom works regardless.
He came from an upper middle class background somewhat similar to myself however, his father was quite the masked jackal and some of those traits would manifest when I would converse with him on different topics.
Opvs Daemonvm: The Devil's Diaries By Draconis Blackthorne