I'm not convinced that banning cards is the way to get rid of so many rainbow decks. Switching out novas for quantum pillars is going to make a full-spectrum deck a bit slower, but its not nearly as debilitating as a mono deck losing all its damage producing cards, for example. In other words, mono decks are often more dependent on a single card than are rainbows.
As far as better vs. worse dogs, in this event the best dog for most of the time was (arguably) ****head and for much of the event he was near the bottom of the standings in terms of dummy points. Maybe there could be a different measure of a dog's power -- something like hp + 5*(str + def + int + luck) and that could be used to determine which dog receives a bonus (if there is one).
On an unrelated note, strength and especially luck are underpowered compared to defense and intelligence. The rule that a losing dog can only deal up to half the damage it receives really hurts the strength stat, since a winning dog can guarantee taking very little damage if it has a low strength. Plus the fact that there is basically no advantage to dealing damage except maybe in the later rounds or just for the sake of speeding things up. I suppose Chromatopup has gotten away with relying predominantly on strength throughout the event so far but he has been walking a tightwire to say the least.
It was suggested earlier that strength allow you to use some upgraded cards and damage would be dependent on which round it was. I could get behind this idea.
As for luck, maybe something like the dog with the highest luck (or a randomly chosen one if there is a tie) receives a free card of their choice each round.