From what i understand, in the original versions of the game you could grab the armor and wear it with the stats, but they changed it long ago so while it is on the enemy it has those stats, but when you take it and wear it it will have lesser stats. So you might grab a chest piece that has 27 armor, but when you wear it, it has 12.
Other posters have said they changed a lot of the armor to also reflect your mana level or other such, so as you add in properties to your chips or such it will make the armor values change. Probably was done this way to make the game more challenging so you couldn't just go out and once you start the game kill an enemy and get the best armor right from the start.
It isn't a big deal as you play you'll find better pieces you can switch out. I usually find Mercenary armor is the strongest. I think i found a Bandit helmet that was stronger than my mercenary armor helmet i switched out later in the game. Common boots often were as good as others.
Just play and have fun, wear what is currently good. It doesn't matter a lot enemies can go through it fast even if you aren't wearking much many like to play with no armor or light armor so they can run around faster. Don't forget later you can boost your armor pieces pretty nice to help with what ever your wearing. You'll want carry upgrades of course to carry more loot, maybe speed upgrades, etc. It's not a huge deal you'll find zillions of armor pieces while playing, and maybe you'll stumble over something thats better than what your wearing.
