I'll write a post about this tomorrow. If someone still has a different opinion on the definition or the wording, speak now or forever hold your peace.
Well, okay, since you asked...
I've glanced through this thread occasionally, as I do with many threads in this forum, but haven't commented because the whole debate seems of largely academic interest to me. I just play Elements, and I build decks to do so, and it really doesn't matter how you lot classify the deck I happen to use.
It has been said that one definition or another gives more power to mono-decks. Well, no, they really don't. I'm not playing "mono-decks", I'm playing this deck I've got right now, and this deck has a certain amount of power. Whether somebody calls it a mono-deck doesn't change that a whit. The whole idea that we have to give mono-decks, as a classification, enough power is a red herring.
My attitude might be different if I were playing tournaments which had rules targeting mono-decks, duo-decks and so on, or if I were trying to challenge someone for one of those titles that I've seen mentioned and floating around. I'm not, though. I have a busy life, with plenty of other things to do, and I'm in Australia which means that the time zone would often be problematic for playing tournaments anyway... Elements is something I play when I have an odd hour to spare and don't have the energy for writing my next roleplaying scenario or coding or whatever. As far as tournaments go, though, the only definition of "mono-deck" that matters is the one used by that specific tournament. If a tournament wants rules about deck types, the deck types should be defined as part of the tournament rules, and other definitions don't matter. A tournament can use the same definition as someone or something else, but that definition should still be incorporated into the tournament rules for ease of reference if nothing else.
And for titles, I don't even know how to go about challenging for a title, so if that's a consideration, possibly the rules of titles generally need to be a little more prominent. Again, definitions for title purposes should be part of those rules.
So again, I come back to these definitions not mattering to me, as somebody who just plays the game.
What does matter to me, though, is deck-building considerations. If I come to the boards looking for deck ideas and configurations, it's because I want to build a deck to play the game, and hopefully to do it reasonably well. The classification system that helps me is the one that allows me to find decks of the type I'd like to build relatively easily, and when I say "type", I mean decks that play a certain way, not decks that fit a specific system of deck taxonomy.
So here's the thing... Suppose I've got this deck chock full of water cards, with water pillars/towers and a water mark to power them all. It works a certain way - pumps out large amounts of water stuff, doesn't worry about anything else. Quanta production and use is very simple.
Then I decide I want to vary it a bit, I think pillar destruction will add to its function in a big way, so I add in three Tridents (or Poseidons). (Not that I actually own three Tridents or Poseidons, mind. It's a hypothetical.) Now I need Earth quanta, and in decent amounts too (especially if all I'm using is Tridents, not Poseidons). The deck still only uses water cards, but at the very least I now have to change the mark, and to make it work with Tridents (not Poseidons) I may well have to throw in Stone Pillars/Towers. For purposes of deck construction, for purposes of making it work so I can just play the game, the strategies and considerations have just changed in a big way.
And here in the forums, if I want help with figuring out how to do it, it's the classification system that directs me towards decks with similar considerations that helps.
Now, I'm not completely clueless when it comes to deck-building. I've played a lot of games, and similar principles from some of those apply, and while I haven't built a lot of original decks, I've built a few decks which have done okay. I know enough to realise that it doesn't matter whether I'm using a given quantum type for casting or activating a special ability, if I need a certain amount of that type of quantum, I have to find a way to get it from my deck. I need to work out whether to add Stone Pillars to that deck, and if so, how many; or do I just need to change the mark? And what do I take out?
At the moment, that sort of advice would be found in at least two of the deck forums: Duo-Decks and Mono-Water. You might call the deck in question mono, but Duo-Decks is likely to have more discussion and examples pertinent to the problem I am trying to solve, because balancing the need for different quantum types is implicit to duo-decks.
I'm not sure that any issue of deck-building is more closely tied to the number of elements in a deck than that of balancing the production and usage of different types of quantum. That means that for me, as just a player, the most useful division of decks into different forums would match the quanta-balance concerns of those different types of decks, so that I can drill down to and examine decks with similar concerns easily.
I honestly don't care whether that matches accepted definitions of "Mono-Deck", "Duo-Deck" and so on. But I question whether use of any of the proposed definitions of those terms has a real purpose for players and deck-builders (as opposed to tournament competitors, competitors for titles, and those engaged in academic debate), and I wonder whether a particular set of definitions would bring the varying concerns a bit closer together.