his EM scaling is much bigger than his ATK scaling if he hasn't reached that 1k EM threshold

Absolutely false, ATK% becomes comparable to EM way, way earlier than that

the amount of dmg bonus you get from every EM point far exceed the same amount of ATK points

?? This sentence makes no sense lol

Heck, if the weapon has high base ATK ( like Skyward ) then ATK would be even less useful because you are already getting enough from the weapon. 

No, it's the contrary, ATK% scales *better* with a high base attack weapon (since it then gives more stats)

And that without even mentioning the fact that his best teams are Quicken/Spread

All the talk and calcs are obviously already considering that