I think CSM Termies suffer from severa issues.
Issue number 1 is lackluster shooting.
Raper ACs wont rape stuff, they are way worse then Assaultcannons/Cyclones of the loyalist counterpart, Combiplasmas to back them up or not. 1shot guns arent as attractive on expensive bearers as they are on cheap "fire-and-forget" units/models.
Issue number 2 is not only bad.
They do have more flexibility in the CC section which is nice, this can cut some corners with the price of the unit, but can also lead to a diluted unit that accidentally lost "important joe" and got boned in CC anyway.
They do however lack the Stormshields which makes Hammernators great which is bad.
Issue number 3 is a sore one.
No useful transport available. LR carries 5 and thats it. Crusaders take 8 which lets you have a beefy unit like 7 + character, thats a lot "more" then 4 + character. Add the fact that the Loylalist LRs are better in general and that the Crusader was built to move, unlike the Godhammer pattern which wastes a lot of Lascannons when it does.
They also lack access to Drop Pod which sucks for controlled insertions.
Issue 4 is somewhat like number 2, not only a problem.
Morale sucks, even more so on expensive units. CSM suffers from bad morale rules now, with a general drop in LD across the book and no SM rules to back it up a lot of your points can be sent packing.
Naturally you can put the boss here to prevent that, but then we are back to 4+boss if you want a ride, or left to hoof it across the table, which isnt what a CC friendly unit wants...
The old tried and true Termicide units are still good, if nothing else you can go for that. There is always some Vehicle that likes it some melta love on the table