About the
, Do you honestly think it can outlifesteal? Lets do the math!
3% life steal on every auto early game your autos deal around 60-80 damage unless you take full AD runes! So you can heal 1.8 life a shot - 2.4 life a shot.
Now lets check the thornmail's BASE DAMAGE. (No armor, even your base armor)
Deals: 25 MAGIC DAMAGE.
So lets do that math!
25-2.4=22.6! DAMN DUDE DOES NO DAMAGE EARLY GAME!
lt's say you have 5 items and a D-Blade with no boots. Your autos depending on the build and ADC, will deal 1.2k at max (Approx.). And you will heal 36 life a shot. (btw this is on a crit, and you will not have this much AD + 100% crit chance so it might not even deal 600 damage on shot!)
While a tank at 5 items will atleast have 150 Armor with that thornmail and your boots.
Lets just say you have bast 50 armor and 100 armor added with nothing else, you will add (25% of bonus armor) 25 damage to your thornmail.
That means at the MINIMUM you will deal 50 damage every auto :O
So do the math, 50-36=14 DAMN DUDE YOU DEALT MORE THEN THEY HEALED! Oh and btw 36 lifesteal with 5 items most likely will not happen in this current meta, unless you are playing jhin or cait and you won't only have a thornmail if they are the dangerous ones.
So yeah, D-Blade doesn't do shit.
And your runes and masteries will not get you more lifesteal then 10%.
10% of 1200, is 120 HP every auto, and honestly if you go full lifesteal runes then you deserve to outlifesteal that item, but STILL YOU ARE LOWERING THEIR LIFESTEAL.