My knowledge of Roman history is pretty good for a layman, but I can't think of a year when there wasn't a dominant consul.
And as a secondary question, in world history was there ever a duocracy (or triplocracy) like the consulate with neither of the leaders being more powerful than the other?
Is that really true though? I seem to remember Caesar causing a bit of a scandal by dominating his fellow Consul back before he went to Gaul.
I don't really understand. The consuls were constitutionally obligated to share power by alternating command every month for a year. This broke down during the crisis towards the end of the Republic because, generally, the Roman Constitution as a whole broke down.