Kiora, Sovereign of the Deep is more concerned with slamming octopuses and serpents than it is swimming with other merfolk, which makes it a technical merfolk commander , but not a great commander for merfolk
When you look at my current roster, you can see: Henzie Bracket 4 High Power Reanimator Hofri Reanimator Bracket 3 Combo Win Cons Joshua, Phoenix Dominant Reanimator Bracket 2 Lower Velocity Aurelia, Law Above Bracket 2/3 Humans/Tokens Go Wide Isshin, Two Heavens as One Bracket 3 Dungeons & Burn Good Stuff Nahiri Bracket 3 Voltron/Equipment Sigarda High End Bracket 3 Voltron/Enchantress So, within those seven decks, you have similar themes or strategies, but with different flavors , and different heat levels
You get a ramp spell early, which helps you get more mana, which helps you cast the more expensive half of the card from your graveyard
This restriction helps you build interesting decks that aren't all 47 Lightning Bolts and a few mountains