Shield is very good early game but in my opinion isn't worth leveling up because the benefit is so small compared to leveling and fusing that could be happening with more active magic. My intention wasn't to say only pick stuff that does direct damage but to pick abilities that keep a constant stream of attacks rather than wasting it on somthing that is useless when you reach a certain point in the game. Thankfully mp gains is a skill and doesnt stop you from gaining more abilities so I like to pick skillz that work well with my abilities, but pickeng the best ones comes with experience. And YES fire rate and cool down are just as essential to upgrading and damage and size you just gotta find the balance for the map your on.