Pure Koa'ki Meiru deck is almost impossible, they are meant to be teched into other decks.
Unless you run Koa'ki Rock Stun deck, which unfortunately needs two Koa'ki Meiru we don't have yet. This box only has Sandman, the deck needs Wall and Guardian as well.
It seems the people here have never really played koaki meiru before. They only work well as pure and most of the good cards are here (only missing drago, diamond core, and doom). And they do better in a format like deal links, especially when synchros hit (which is the era they’re from)
Running a pure Koa'ki Meiru deck can be fun. Iron Core can be searched, Urnight can be searched with Tenki (if they release it here) and also swarm the field, its continuous spell (forgot the name) can massively increase all Koa'ki Meiru's ATK on your field up to 1500, Maximus is a good card remover and powerhouse, Doom and Dragon can negate Light & Dark monsters (here's kinda useless for now)
In short, pure Koa'ki Meiru has power, search-ability, swarming monsters, and card remover. You just need luck to draw them correctly (which, in this case, is pretty much the same for most decks)
Koa'ki Meiru is just so much better played in monotype deck than in a pure Koa'ki Meiru though, since monotype deck would give more ammunition to keep the Koa'ki Meiru monsters alive.
The best Koa'ki Meiru decks that aren't just pure Rock stun tend to only use the Rocks and Beast-Warriors. (Maybe splashing in one or two tech ones that aren't type-reliant, like Maximus, Ice or Tornado.)