In general a rainbow bloom will out perform a gold unit. If a 1/1 rainbow bloom is better than a 5/4 gold bloom really depends on the units involved. I general I would consider a 5/4 better, especially since we are still lack blooms. I try to make all my rainbows at least 3/2 or greater so in my case my rainbow wall tends to be better...

A lot of people want lots of rainbows for waifu purposes... its not like the game is overly challenging (yet), although there are some times where power is very important (current event)..