Codex Creep? Maybe it's me but I'm just not seeing it. I read through every codex and play around with different builds. I'm still relatively new to 5e but I played a lot in 3rd & 4th. I think a lot of people confuse different with better. Every rules change makes some things better and others worse. So I have a Darwinian attitude of adapt or perish!
Look at the Space Wolf codex. From all of the belly aching you would think that the wolves would never lose a game. That ain't happening.
I'm even starting a Dark Eldar build now for 5th. At the moment I think the Raider force is one of the better competitive builds in the game.