Energy Aura?

To be entirely fair, Shield provides mitigation in the form of +HP, resists, -dmg, and knockdown. SR has defense that can't ever be debuffed away and the scaling resists that certainly count for more than you're giving credit for.

I hear what you're saying, though. If I'm going to say you can't compare the defenses without taking into account the sets they come from, then I have to take into account the entire set.

That said, I have an EA stalker. It fits my concept better, it's a lot of fun, but even with all the bells and whistles included, I'd be more survivable with /SR. That's coming from an academic numerical analysis as well as gameplay experience points of view.

That's why I stated "substantial" for those effects. The effects you mention in Shield are nice, but they're nowhere near as strong as the outright defense. For SR, the scaling resists are, once again, nice, but they're not going to provide quite the same degree of additional survivability as the Invuln resists do. The DDR in SR is largely there due to the fact that the set is almost entirely reliant on defense (and you can generally gauge how reliant a set is on defense by looking at the degree of DDR the sets get; both of those sets have "high" DDR demonstrating higher reliance on defense and lower reliance on their other mechanics).

That's a point that we can both agree on though I don't think it's really the fault of the set being typed defense based rather than a positional set. In fact, if you use the IO equivalences (melee = s/l, ranged = n/e, AoE = f/c) and switch the defenses out, you'll achieve only the slightest of increases to overall survivability (using Arcanaville's survivability spreadsheet, the changes would make the set only 4% more survivable).

The weakness of the set isn't simply a question of typed versus positional. The weakness of the set is more substantial than simply a difference in what defense you're getting. The weakness of the set is based in the fact that the set simply doesn't have enough going for it and it needs an outright buff (preferably in the manner I've suggested as it would allow for proliferation rather easily) rather than a simple exchange.