I agree that it's a much smaller problem than the Spire set, but I think you might find it creates a slightly bigger imbalance than you think. This event will be quite difficult for people to complete the set by default, unless they give a lot of thought to beacon selection and are active enough to complete the quests and collect all the junk, amongst the non diamond spenders. I believe that the average player will not complete the set in this event. It would be interesting to see the numbers come the end (which we never will), but I wouldn't be surprised if less than 20% of players taking part in this event don't finish with a complete set. However, 95% of those players will have picked up the first couple of pieces and probably enough to activate the full marble bonus.Most people will not have an imbalance at all, only special cases will get an uneven number of buildings.
So we´ll have very few towns with only 1 imbalanced set, instead of everybody having multiple imbalance causing sets.