Question about DEX

The usefulness of DEX is entirely dependent on the class in question. If you're an Archer, it's your main stat and the primary attribute contributing towards your damage. If you're a warrior, it has a few purposes; [1] it contributes greatly toward accuracy, [2] it increases base damage which leads to more consistent damage, [3] some equips (like stonetooth sword) require DEX. If you're an assassin, DEX's only real purpose is for wielding equips (as Lucky 7 and triple throw do not consider DEX is their damage calculation), so it's usually only utilized at higher levels (when stronger equips require DEX). Compared to assassins, DEX is slightly more useful to bandits, as it helps increase base damage for more consistent damage as well - though DEX is still usually kept at a minimum until needed for equips.

High avoidability usually has no weight in determining your stat build - it's more of an added bonus for certain classes (either way, LUK contributes more to avoidability than DEX for every class except pirates).

Hope that answers your question!

 

Gladly
This may be more than what you're looking for, but you can find a breakdown on most of the game mechanics here:
https://ayumilovemaple.wordpress.com/2009/09/06/maplestory-formula-compilation/

If that's a bit overbearing, I put together a general guideline:

Spoiler