How much of a Stat is 1 W.Atk?

Not necessarily =/= completely irrelevant.
If you don't level up most likely you don't have much of a liberty to add more stats. If you level up most likely you'll want more dmg. But yea, most likely =/= definitely either, I'm just pointing out a random lame thing.

Stereo's estimation can be taken into consideration, around 120 it should be 5:1 whereas 40~70 should be 3:1. Just for comparison.

It's irrelevant because it's not in the equation needed to calculate how much str = 1 atk (for warriors). I could not know a thing about someone's level, all I need is their strength and attack. Hence it's irrelevant.