That's actually improved a lot recently, there are top tier decks for almost all of the summoning types at the moment.
It helps that the new anime actually balances between the types rather than everyone just hopping on the Pendulum bandwagon.
Madolches are partly fairy but I don't think anyone is using a full mono fairy deck.
I am extremely grateful for that. It isn't that I didn't like Elemental heroes, in fact I am a fan. Heck Elemental Heroes started off as a patch to Fusion decks because, well, fusions were mostly pretty useless outside ways to instantly summon one. It just ended up unbalancing them to heck.
-Heck if you want to be technical the Elemental Hero era had the MOST variety of decks ever introduced. While the Synchro era had the least.
It is that the card game ended up boiling down to what usually amounted to one maybe two types of deck... and maybe one more if an exploit was found.
How many players do you have so far anyhow?
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Even going further Tuner cards weren't a bad idea either and the "contact fusion" was what I believe was the inspiration. The point of Tuner cards is that they are fusion monsters without the need for polymerization.
The problem was that when they made them, they seemingly made them with the intent to outdate everything that was previously made before it. They became "Elemental Heroes except even better" rather swiftly and even now they are likely never going to remove themselves from the game. To the extent where I believe they had to remake elemental heroes to not be completely outdated.