I think you’ve misunderstood the Cabal’s post-action report. Assuming you’re referring to Ghost Fragment: Cabal 3, the report states:
"Guardians can be rebuilt after even total disintegrative trauma. This capability is provided by a small autonomous drone unit called a Dead Person [trans. unclear]. The Dead Person conceals itself during combat. It is not a viable target for direct fire. Saturation attack by artillery/heavy air/orbital fire may have good effect (although Guardians transmat frequently and refuse to assemble into large formations).
Solitary Dead Persons have been observed in all areas of operation. The relationship between solitary and paired Dead Persons remains unclear."
The key here is the phrase “The Dead Person conceals itself during combat. It is not a viable target for direct fire.”
This means that, because Ghosts remain hidden while their Guardian is in battle (unless they emerge to resurrect them) the Cabal can’t target the Ghost directly. The strategic consideration is likely ignoring the Guardian and handling the Ghost first, but that’s impossible, since the Ghost won’t show itself unless it decides to revive its Guardian immediately.
The author goes on to say that saturation artillery might be a solution, since the first volley would kill the Guardian and the second its emerging Ghost, but such expenditures would be costly - not many Guardians killed for a lot of shells spent, owing to the fact that Guardians rarely assume large formations.
However, there have been times where Guardians were forced to assume large formations and sit still, without transmatting freely, to defend a specific point. One example would be Twilight Gap, where Fallen artillery were able to take advantage of that. Guardians were holding the line and couldn’t evade or sow chaos they way they normally did. Shaxx mentions implementing Control mode in the Crucible to teach Guardians how to defend a set location, and one of his reasons was the casualty count at Twilight Gap.
As for damaging a Ghost with direct weapons fire, we have a perfect example in Felwinter’s execution of Citan.“Felwinter’s shotgun cracked like thunder—once for the Warlord, and again for his Ghost.”
There’s more than one way to kill a Ghost. While the Cabal concede that the Hive’s methods are tactically superior, if anyone - Cabal, Fallen, Hive, or Iron Lord - fired on a Ghost, the Ghost is just as susceptible to being destroyed as anything else.