Sure, it makes sense in that context, and I know you often like to use Saber specifically against Cerberus.
Personally I play this setup lobby set to U/U more than 95% of the time and I rarely host. Makes little sense to take a power amp mostly just for Phantoms; ability to take some hits is generally more helpful. And it's not like you never go down either. 
So yeah, if Phantoms are a primary concern, 6B is probably a better choice, I wouldn't disagree with that (at least it gives you the option to take the power amp). But with 6A Phantoms still aren't any sort of weakness for this setup, it just takes another shot to finish them off. A long time ago Saber GE was one of my top 3 go-to kits on Plat, and I never found killing Phantoms difficult (though they're always nasty when they're shooting at you, of course).
Phantoms are never gonna be a weakness or a real problem for a GE, that's sure

However, there's a difference between dealing with them easily and eating them for breakfast. If you can kill them fast enough, phantoms become awesome to drain the wave budget.
And the difference is not only one shot more, but also how easy is to pull that shot off. If your OL doesn't drop their shields, they won't get staggered either. Which makes aiming for their head definitely harder. Now, I don't have much experience with a Saber GE, but I would imagine that is an even bigger problem than with a Talon GE, because of the spread and shield gate ignoring capabilities. "Problem" is a relative term, alright, it's still easy to deal with them without a power amp. It's just easier and faster with one

Having said that yeah, the power amp loses a good portion of its appeal against the other factions. Although it's still useful, mostly because it increases the damage done to the second (and third) targets of OL.
While yeah, we all know that I drop very easily, I feel that the GE is one of the kits I drop less (if that's even a thing... XD), even without a cyclonic... At least in good lag conditions. The combination of overload super CC, HM and shield restore via turret makes it hard to die, really. So I think that if you know you're gonna have a good connection and/or play against cerberus, a power amp might at least be as good as a cyclonic. Also because you can stop Phantoms pew pew whenever you want to, which is very useful.
That said, even some slight lag can easily change that, so I agree that a cyclonic is the best choice if you pug U/U, and it's in fact what I usually bring, too.
I was thinking of the loss of DR once you detonated Reave
As far as I know, you don't lose your DR when you detonate reave... Do you? Besides, it's not like reave DR alone on a Drell is crucial to your survival...
Nope, OL it self don't stagger them at all, so stop spreading these malicious lies before you get some poor dumb pug bastard sync killed! 
Think it's just the Falcon (its great against phantoms), afaik at least fire explosions don't stagger them.
Actually, overload does stagger them each and every time it drops their shields. Which, as I said, is one of the main features of being able to one-shot their barriers, since you have a way of stopping then cold whenever you want to.
FEs stagger them as well, although I'm not sure about TBs.