First off, "SS isn't balanced off raw stats" is a funny thing to say when you just used the examples of HBI (basically free OP) and Heavy Armor, and go on to talk about venting flux, all of which are in fact raw stats.
Second, "balanced off of weapon behavior and the ability to vent flux" - to consider just one case, what exactly do you think the whole thing about Reisen (M)'s four large + four medium ballistics running off better-than-Radiant flux stats (for 3/4th the DP and no Automated Ship restrictions, I might add)
is?
Three:
Raw armor values are kinda pointless, because the important part for a capital ship is whether it can shrug off a reaper torpedo or hellbore shell. If it can't, it needs to keep those shields up, which means it's always going to flux out.
This is just plain false in the way implied; if it weren't, shield shunt Onslaught would not be a thing.
It turns out that sufficiently high capital armor and hull is indeed what you need to shrug off Hellbores and at least not die immediately to Reapers (assuming your PD doesn't stop them, which turns out to be a lot less common when you can throw vulcans and flaks at the problem). Armor is the thing that lets you lower your shield even when under fire without promptly dying, up to the point of venting under fire if necessary; in fact, I would say that this is
the purpose of armor for most ships.
As for "always going to flux out": again, misleading at best. When you're a capital that can run multiple large and medium ballistics at flux neutral, it's much, much harder to flux out because you can use your entire, massive, capacity bar to absorb damage, and vent it off that much faster after it does build up, and enemy ships have a much harder time closing enough to use their weapons to begin with. Almost 30k effective shield HP that can be active vented in under 17 seconds (stripped Reisen(M) and Rillaru(SP) both do this) is a hell of a drug. Even if you aren't anywhere close to flux neutral, the difference between fluxing out in 20 seconds of combat instead of 10, or 40 instead of 20, requires no description.