And, tbh, why even take them, if you cannot buff them properly?
Because they don't need to be buffed to be good.
The only buffs they can get are:
+1 to hit + Run and charge (this is the big one) - skink priest
+1 to save - also skink priest, and also notable because they have a 4+ save base
6s to wound cause a mortal wound - pretty much worthless for them - Starpriest
+1 attack in melee - decent buff from steg chief, though probably worse than +1 to hit in most cases.
3d6 to charge - Not really needed with running and charging, but the spell for another +1 to save is nice - Starseer
In a thunderquake, you can bring them with the steg chief, which is nice for coalesced lists, where they're already getting an extra jaw attack, for potentially 6 jaw attacks with the battalion. 6 jaw attacks makes 3 salamanders put out ~30 damage at rend -2/mortal wounds with their shooting + melee without the +1 to hit. +1 to hit at 5 melee swings puts them at 33 damage; less mortal wounds, but more at -2. Without either buff, they're doing ~27 damage. With no buffs at all, they do ~21 damage in starborn, or 24 in coalesced.
The buffs just really aren't all that important for their output. Adding another salamander would technically always be better for output than a buff. The effective range buff from running and charging is probably the one that matters the most, with +1 save being the second most valuable, since it should be fairly easy to put them in cover, and a 2+ save is strong.