I think I explained it pretty well but here goes again.
1 str = 3 inflated points of melee.
these inflated melee points are greatly reduced by pdef meaning your damage will be weaker as more and more armor comes out.
Now you might be asking yourself if all points of str are created equal why are guards/defs so good? the answer to that is buffs.
You pop cs or fixation and now you have the massive inflated melee needed to hit through that pdef with ease.
Sadly your avenger doesnt have that (I guess ruin trap could take care of some of this inflated melee pdef problem but traps die in 1 hit) so you need PURE ATTACK! and lots of it!
the best way to gain pure attack is to get boss drops. Cheapest is silva feather (has 300 base attack) but if u are low on the cashes and only wana get +12 or so then I would advise getting rulers if you can. Anyways if you got the cash and u buy 4 silva +18 ur looking at over 2k pure attack right there!
the rest of the stuff just adds up 50 here 100 there so on and so on.