Yeah I really don't think there's a plan behind it. They have confirmed that step 1 in the process is ALWAYS making a new model, then they give the new model to the lore and rules people and have them make things for the model, never the other way around. So I can imagine it gets a bit tough trying to constantly slot new things in.
It's gotten better now that they've actually hired a huge number of playtesters, but because most of those playtesters are top tier tournament players I'm not fully convinced the balance is better as a game, as opposed to better for competitive.