6 Isn't a standard for Dominion I believe. At most it's 5 I believe. 4 Paths at 3 would be a better estimate (as that is primarily what Rainbows use)

Dominion isn't as useful to Rainbows as it is to Combat Pretenders, because Rainbows do not fight initially, only when they are ready to handle situations and spell research is ready. Whereas the point pouring into Combat Pretenders it to have an immediate economic advantage, wheras with the Rainbow it's a potentially significant gem advantage.