Always stoked to read more theorycraft. Yep, I assumed Evasive Action to be better purely because 50% to DR has been proven so powerful in the past (along with the 50% opposite from Target Analysis). Happy to be proven wrong, but yes as others have said.. pick both armour skills. The 50% maneuverability buff should not be discounted as that's pretty useful on its own, but it's more of an utility-class bonus, like Ordnance Expertise's projectile speed.
On shielded ships with Defensive Systems, it's a bit of a toss-up still if you also want to double-dip with armour skills. On a front-shielded Medusa or Aurora I'd pick EA in a heartbeat. On frigates and other agile ships that are not so front-locked it's probably IM. But generally for player-controlled ships I prefer to stick to one defensive type and getting more damage and offensive skills instead.