Lately the Spell Slinger has been on my mind. So, I've been thinking.. What makes it so terrible?
First, what do you lose.. You loose all 0 level spells. You lose your arcane bond. You lose your school bonuses and bonus school spell. You lose two more schools (I know you can still memorize those spells, for two slots instead of one one.) You lose scribe scroll.
You gain a very dangerous way of firing spells out of your gun, gun prof, and gun smithing. You can also sacrifice spells to enchant your gun.
Overall, it feels like a waste.
So, how can we improve it?
Step One -
Instead of losing 4 schools, and cantrips -
Diminished Spell casting - You cast 1 fewer spells per day of all levels.
School of the Gun - instead of choosing a school, you are part of the school of gun. 2 schools are your 'banned' schools.
Truely, you're getting a 2spell per level hit here. You're still specializing in a 'school' but you aren't getting the bonus spell for it.
Then, the first power. You're sacrificing a spell to add an enhancement bonus onto your gun. Why oh why, do you also sacrifice all your cantrips too?
Lets say, you can't use cantrips on it. Done. Now is it needed to limit it to a number of uses per day beyond what the current amount of spells you can cast is? Diminished spell casting + not getting a school bonus spell, hurt that pretty well. So, lets keep that as is.
Sacrifice a spell, get its level in +X bonus. Simple. Done.
Now Arcane gun.. well, you ain't getting an eighth level ability like all the other schools do. Nor are you getting a basic ability from the school. So, I believe that is done too.
You can also select grit feats in place of wizard bonus feats.
Nothing to add?