I think the rules are very clear on this. Each card in Elements either belongs to a specific element or 'Other'. When the rules say you must have at least half of the cards from your own element, that's exactly what it means. I really don't see where there's room for interpretation.
For example Quantum Pillars are 'Other'. They are not Water, Fire or Death. They are 'Other'.
It's fairly clear, but I'm still slightly confused. If I have a deck of 30 cards and 10 pillars, do 15 of my non pillars have to be my color, or five of them? I assume from your post that it would be the first, but I'd just like to clarify before I go too overboard.
The issue I can see with the pillars not counting towards your color is the forced bulking of otherwise sturdy decks. One perfect example would be the graboid rush deck (x6 graboids, x6 shriekers, x18 stone pillars). Since I'd only have twelve earth cards and eighteen "other," I'd be forced to pack in at least six more earth cards, for no good reason.
Any insight would be appreciated.
PS: I have no issue with the "balancing" of this event. It was brought up, and then you explained that it wasn't exactly meant to be fair, but not made unfair intentionally. Well done.