@KnightHarb1nger For the weapons, light is usually the most versatile choice since most Falspawns have light element as one of their weakness element. Of course there are many enemies who don't have light as their weakness, light weapons won't have an advantage against such enemies, still they have a good number of enemies they are effective at. So if you have to choose one element for your best weapon, usually light is a reasonable choice. But for weapons aimed for some specific purpose, they may have other choices.
Speaking for the units, I'm not perfectly sure about what I'm going to write here, so people who know better, please point out if there are any mistakes
Element Resistance of units only works for enemy attacks that specifically have that element. For example, some of the attacks of Dark Falz Elder freezes us, these attacks have ice element so ice resistance on our units work against these attacks. But all other attacks of him are non-elemental attacks which are either of Melee/Ranged/Technique. Elemental resistance won't work for such attacks.
So having better elemental resistance stats on units is useful in certain situations, but that's not a top priority issue. That's what I understand.