No shields method makes missiles/torpedoes and fighters very effective against your ships.
Luckily I can bring so many PD coilguns to the fight and pack my ships in so tight, since I gave them to every DD variation, at this point enemy ordnance basically has zero effect against me. I get hit by those crazy Marauder torpedoes once in awhile but that's about it. My main problem has been against Marauders in general, since they have some terrifying beam weapon on their capital ships that tears my DD's up. I'm hoping my new Railgun armed Heavy Destroyers will help deal with those situations.
Concentrating on shield-piercing weapons should be a viable strategy, but I don't know that forgoing shields yourself buys you much, except more ammunition for missiles. I guess you can double up on reinforced bulkheads, which might be favorable if you rush to the next armor level.
Yes, I've been favoring armor research and actually eschewing extra ammo for just more bulkheads. I suspect that if I didn't have such an economic edge my strategy wouldn't be working but I afford to trade DD's for anything else the enemy throws at me at about a 2:1 ratio and still win.
My intent is that unshielded builds should be viable, in some situations, at least.
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I'm also fine if the answer is that at some point I'll need to bite the bullet and add shields, and techs just delay the point where that needs to happen. My strategy worked better in the early game but appears to have been become weaker as everyone else trots out better weapons.
-Will