Best Post-Rotation Deck to Learn Competitive Fundamentals?

Returning player. I used to play straightforward "attach energy and hit them" decks like Blacephalon GX and Pikachu Tag Team from SM era and Miraidon/Chien Po/Charizard in more recent times. My results were very mixed/bad at higher and higher competitive levels because I didn't actually do anything that better players do. So, I'm looking for a deck that specifically forces me to consider all the competitive fundamentals: efficient searching to determine prizes, prize mapping, sequencing, etc. Before it died, I think Lost Box was a good example of this because it required this, dialed up to 11 out of 10. Is there an expected deck post-rotation that's kind of like this?