Jacob was a Biotic, Biotics almost seem to function like computer game wizards, barriers (magical shields) in place of heavier armour.
Nearly all the Biotic party members have light or no armour.
I'll point out that in ME1, biotics still wore armor. Granted, it was lighter duty armor, presumably to help mitigate exhaustion and over-exertion, but they still wore it, not only for its ballistic protection, but for the other benefits it provided. They also wore helmets whenever necessary, either in a firefight or in a toxic or harsh environment.
Barriers don't protect you from toxic environments or places like Luna with no atmosphere.
Also, ME1 established a very reasoned system of layered protection via barriers, shileds, armor, and the under-armor, and it made good logical sense.
And as an added point, I'm guessing that every biotic in the Alliance is expected to wear armor. They don't get a pass, nor should they. There's a reason why nearly everyone in the known galaxy wears a hardsuit, biotic or not.
I get your analogy, and I'm not saying you're wrong. That's probably what was in their heads when they decided to abandon armor in favor of cheap T&A and beefcake. The problem is that a military space shooter and sword & sorcery RPGs aren't directly relatable. You can't just make them wizards in space, even if that's essentially what they equate to from a purely gameplay perspective.
Gameplay aside, nothing else about them is relatable, and therefore Bioware should stop trying to use the rules of Dragon Age and Baldur's Gate to determine how things work in a futuristic military sci-fi environment. Not everything, or even most things translate at a 1:1 ratio.