So what would you take out to make room for proper AT? What good AT units do we have?
I'm still looking at this as a whole. The consensus is that the codex options are not good enough "for competitive play". However, I grew tired of tournaments long ago (been playing 20 years) and don't want to use that as a rational to buy forgeworld units that cost an arm and a leg while still dying easy and making all my opponents hate me. I'm also avoiding using CSM allies for the time being because I'm already using two books (TSons + Daemons) and don't really want to use a third, though to be fair, it is an option.
Given those personal constraints, I'm looking at the obvious: options in the TSons codex are forgefiend, maulerfiend, hellbrute, or pred for dedicated AT. Daemons have either buffed mass shooting or Exalted flamers.
Forgefiend and maulerfiend I ruled out. They cost too many points to run multiples without sacrificing the main strengths of playing TSons in the first place (high rend anti-personnel fire en -mass), and maulerfiend needs multiples in order to get to combat. Exalted flamers look good at first, but their damage output is too low to work in low numbers.
What remains is what I'm using / would recommend. Hellbrutes, Predators, and massed daemons fires. Hellbrutes and predators are straight forward: they are buffed by spells, strategems, get-rolls from sorcerers, etc. Give them Las and missiles and point them at the enemy. Just make sure to keep them bubble wrapped and positioned to avoid enemy fire.
Daemons have the spell 'flickering flames', which opens up some tasty options. Combine it with the herald's aura, Cast on 30 horrors, and you have 90 shots that can wound most armor on 4's. Cast on flamers, and you can get up to 12 d6 auto hits, wounding on 4 with ap -1.
My take is combine these elements: Use daemons to do mass wounds, hellbrutes and preds to do some heavy hitting, and finish it off with smite.
If this doesn't work for you, you can always buy the latest ultra-killy turbo laser spammer 5000 from forgeworld, or ally in havocs or obliterators from CSM.