When you're discussing decks in a forum like this, you're talking about game mechanics more than storyline or art, straight up. No one cares what a card looks like -- the only thing they want to know is "can I put it in my deck without adding different towers/changing my mark?".
If the card is Purify (elite) or Animate Weapon, the answer to that question is always "yes". Therefore, in the only terms that are relevant to any discussion we would want to have, Purify (elite) and Animate Weapon are "Other" cards and can safely be put into a mono-deck without bumping it into the duo- and trio-deck sections.
Any other method of sorting those cards is plain silly, as it would turn a Seraph-style Explosion/Morning Glory/Miracle deck that runs a Purify (elite) and a few Animate Weapons into a "rainbow deck" despite the fact that the deck only runs Light and Fire quanta. In other words, the entire logic behind Rainbow decks (spread out quanta use to make maximum advantage of the variety of quanta that rainbow decks produce) utterly fails to apply. The deck is in every reasonable judgement a duo-deck, because duo-deck logic (keep one element minor and use the mark to power it in order to attain consistency from the main element) does.
It's not semantics -- it's the root of the way people address deck construction.
And yes, if for some bizarre reason Zanz created a bunch of cards in each element that all required only Fire quanta to use, then creating a deck of all 12 elements that used only fire quanta would still follow basic mono-deck logic, and should be put in the mono-deck section.
