The best use case with Kairyu-Shin is that its a Level 5 and can help access the K9 engine for K9-17 Ripper for a monster negate in the hand or GY, which can come up in most duels
This is helpful, as you can Special Summon either Mermail Abyssmegalo to attack for the win or Mermail Abysslead to Tribute a Mermail monster and send 1 random card from your opponents hand to the GY
Meowth can be obtained from Mega Rising: Mega Altaria pack in the Mega Rising set
It's just extremely good and efficient at what it does and that's all it needs to be
If you're going to cast Ghalta, I highly suggest having some kind of boardwipe protection first like the Skullspore Nexus just before this, or at least have something that gives your creatures haste so that you don't give your opponent any chance to fight back
While the allure of Timetwister is very strong due to its status among the Power Nine, it can actually wind up being a difficult sell for decks that want to use cards in the graveyard