I think your confusing the guy. Let's break it down simple for you.
Armor and Shields contrary to popular belief aren't much different. They have to be completely breached before they are destroyed. Problem with armor is it is possible to even partial damage it while shields just regenerate after the battle. For the purpose of further explanation I will use the MK 1 Crystalline armor plates for comparison. For shields I will use a MK 21 Adv Electromagnetic shield .
15000 armor
15000 shield
Now vipers will damage these both exactly the same way. A MK 27 Viper has 15000 attack not including any bonuses the ship will likely have. Enough to bring down 1 module of either of these if it hits right.
Lasers will work different. A MK 7 laser has 15000 attack. However even with a good shot, not including bonuses, it is only going to do roughly 7500 to the armor. To the shield it will easily pierce it. To get through the shield you only need a MK 2 laser. For the armor you would need a MK 17 laser.
Now railguns also work different. A MK 2 Railgun has 15000 attack. Against that armor even a MK 1 will do nicely. Against shields you would need a MK 7.
The problem with both Armor and Railguns is the fact that they are both expensive to build. When it comes to cost effectiveness, your better off going with shields and vipers. Why vipers? Because for COMs they are equally effective against both shields and armor. Enemy COM ships of course have both. You can also just marine up if you prefer. When designing a PVP oriented ship you want lasers. Most people just aren't going to use much in the way of armor. Lasers while more expensive then vipers, are cheaper then railguns and are what is needed to get through enemy shields quickly. Yes if the enemy has a lot of armor you may need some railguns. But the odds of that being the case isn't very high simply because even with PVP ships, most of us just don't want to shell out the cost for it. Granted we can easily build some of that with stuff we get from nest. But if we got to repair it, it is going to be pretty annoying. That is why I worked on phasing out armor. It is even more annoying that we have to repair it to even remove it. You should be able to remove it without repairing it. Only it would be worth a lot less in that shape if you were to sell it. Which of course makes sense and would be fine with me. There is one thing I want to comment on now before ending this.
15000 armor protects against 30000 damage.
Only if the 30,000 is from a laser. I haven't seen anything to prove otherwise.