The real good investment is backrow (battle traps excluded), backrow carries tons of decks, konami rarely ever limits staple backrow (last one was treacherous and that happened like 2 years ago)
Only good investment backrow now is Karma cut. Look at how Fiendish chain, CC, floodgate etc. have very few uses now. Konami is now starting to release much bette backrows than the previous like Book of moon so investing on backrow might be a waste since for how its going RN we can espect the likes of Cumpolse in near future.
Those you mentioned are not favored anymore but are still prevalent. Or is it that decks just run 3 karma and nothing else just because they aren't at karma level? It's not like you can run 6 karma cut. Floodgate, fiendish, Raigeki, ballista, canadia may not be as good as before but still see play at the very least as filler but a pretty decent filler at it