Well, yes and no. I've mentioned before that our Starborne/Coalesced split coincides with flat bonuses for units in each through special rules, and we'd be remiss to forget that 3rd Edition is likely going to be paring those down based on current trends. As pointed out by others, many of those "good" Seraphon units are heavily dependent on subfaction bonuses to be what they are, and so it follows that any changes to those subfaction rules have the potential to either make or break them without ever having to touch the warscroll itself.
It's for that reason that I'd rather see Starborne and Coalesced be treated as functionally separate factions within the Seraphon umbrella, even if it means they get a Horus Heresy Legiones Astartes-esque "We function very differently from one another despite effectively using the same models" shtick. We otherwise simply don't have a guarantee that we're going to be keeping any of those rules transitioning into 3rd.
All 3.0 books have subfactions that benefit specific units. It's not something unique to seraphon and we see all of our good units used across both sides in comparable numbers.
If I haven't said it enough, our "good units" aren't dependent on Allegiance abilities. Our Allegiance abilities are just so good that it makes our good units even better. As evidenced by most of our good units being used in all subfactions.
Bastis were a staple of dracos tail lists. 30 skinks are powerful in thunder lizard or fangs of sotek. Salamanders are a powerful asset in coalesced lists just like they are in starborne. Are there a handful of units that are better in one or the other? Of course. But just like redeemers are better in hallowed knights or pigs are better in bloodtoofs, it's the same idea.
Will our 3.0 book be paired down? Possible. But if it's paired down in a similar way there's even less of a reason to seperate them as there would be even less Allegiance ability buffs to pull them apart.
We have A quality warscrolls being supported by A+ quality Allegiance abilities (and a lot of them). If we got less Allegiance abilities there isn't really that drastic of changes that need to be made.
Like I mentioned in a previous post, the sheer number of command abilities seraphon has access to is fairly unique and not something present in 3.0 books at all. I'll be very interested in seeing how that shakes out.
But at the end of the day, if Starborne lost everything but teleport or summoning and coalesced lost everything but -1 damage... we'd still be really strong. Hell, you could probably also remove all of our command abilities outside the priest one and we'd still be really strong. Saurus would suck even more than they do now, but thats kind of its own rats nest of a topic.
For what it's worth, i think if you made warriors a 3+ save they'd be instantly really strong. The last thing seraphon needs is another unit that does a ton of damage.