Out of the armies you mentioned, no one plays world eaters or Emperors children. Khorne beserkers are taken as part of alpha legion, as they can get turn 1 charges. Otherwise, chaos armies are built mostly with cultists. I've not seen basic chaos marines on tables, or noise marines.
Death guard armies are just plauge zombies and warmachines. Again, no one takes anything in power armour besides heros.
It's just the fact that power armour models are not resilient enough for their cost, and die too easily.
Primaris marines are more along the lines of how marines sound be stat-wise, but they lack affordable transports.
The other big reason for screens, is that so many armies can deepstrike and charge turn 1, and you need a buffer from them charging and wipeing out your valuable units, and to also fill space to limit where deep-striking units can go.
It's hard to build a list without units to either 1) block turn 1 charges, or ,2) fill space to push back the 9" deployment for deep-striking units. Units which fulfil this role need to be expendible, and fairly cheap.
Now, I do see a lot of potential in rubric thousand sons being very competitive on the table. You just need to take support for the thousand sons. It's also 100% in character for chaos warlords to bring expendible chaff to soak bullets for them :-), and some ranged support from some sort of battle tank.
All you'd need is one squad of something just to keep your opponents honest, and it'd help keep you away from 'gotcha' moments. I know you hate the tzaangors (for whatever reason), but there are other options. Cultists, horrors come to mind. Even chaos spawn can work in a pinch.