All-in-all, the gameplay balance between the utility of shields and armor is quite good.
I want to reiterate what I think is a key premise of my analysis, with emphasis added:
I honestly wonder if shields are possibly too strong after the early to mid tech levels, since they do not scale linearly, but given that for armor a practical rule of thumb is that it takes eroding ~50% of a ship's armor before internal damage becomes frequent and catastrophic - a very approximate rule, but sensible in general - if shields are even "only" 50% as size-efficient as armor at typical tech levels this would make them in practice just as good, and then better because of the additional advantages of shields (ignore weapon damage profiles, recharge vs repair, corbomite vs duranium to build, etc.). I would guess that probably to be reasonably balanced one would expect shields to be roughly ~33% as efficient as armor per ton, somewhere in that 25-40% range is probably reasonable.
While shields are never, ever, as efficient in points-per-ton as armor (as long as the tech tree is not extended by DB modding), it does not have to reach this point to eclipse armor. This is because, as a rough rule of thumb, once about ~50% of armor integrity is lost a ship is sufficiently exposed to internal damage that the armor is combat-ineffective. This is due to the stochastic (random) nature of weapon damage and armor damage/destruction. This is not a hard rule, particularly at the extremes (1 layer or 100 layers, for example) but it tends to hold up for most
typical armor schemes used in ship designs by both players and NPRs.
What this means is that if shield efficiency approaches or exceeds just 50% of armor efficiency on a point-per-ton basis, shields are going to be broadly superior to armor except for relatively niche edge cases and commercial ships which have no option to mount shields. Note that this is separate from the discussion of the other pros/cons of armor vs shields - recharge vs repair, the ability to blunt penetrating weapons, and so on. The point I am making is that while these are good arguments for using shields when they give, say, 25% to 40% of the efficiency that armor does, once they exceed this range - which they definitely do - shields are already dominant even without all of these other abilities, tactics, and other advantages.
Thus I would agree that shield/armor balance is generally reasonable at low to mid tech levels, but once we start looking at shield generators with sizes of around 40 to 50 HS which approach or exceed that 50% efficiency, armor falls off very badly in relative effectiveness. I will say that this isn't necessarily a bad thing, as evolution of different systems in relative effectiveness at different tech levels is one of the fun parts of Aurora, but whether good or bad we must acknowledge that shields beyond a certain tech level do outperform armor almost totally.