Moriis cards very rarely feature powerful or impressive Pokmon
As for this being a starter set, I think she's fine, but I can't say I find her very impressive in any other capacity
Eventually, I learned how to interact with the combo, and the first time I beat that deck was one of the greatest days I've ever had playing Magic (after I learned to beat that, he brought a Stasis deck, which caused more table flipping but also another great experience once I eventually figured out a way of beating that deck too)
You wind up with one set that can do things the others can't, forcing players to counter that set with other cards from it, and generally limiting the creativity with which one can effectively play the game
Limit it to two or at most three types to create a consistent list focused on executing the necessary moves for victory
However, Tiamat almost wants to be removed , as it will allow you to keep using its enter the battlefield trigger