Without a strong understanding of the magic you are using spells can easily backfire. Imagine having to draw out an intricate pattern in your mind, and if there's a single flaw it explodes in your face. Not to mention, I don't think that it'd be all that great to have to rest after every single battle. Warriors can sit down for a while to get their energy back. But using magic is a much more serious drain of energy. It doesn't just make you tired, it drains your very life. Therefor, training is much, much more difficult for a wizard. To get stronger an archer simply has to practice their aim and a swordsman has to practice their technique. Wizards however to become stronger, have to learn extremely complicated runes by heart, AND they have to increase their very life force.

Imagine a drawn out battle. Archers can fire as many arrows as they have, and can even use ones given to them by others. Warriors can fight as long as they have the strength, and the most they need to keep going is a quick breather and they are back at it. But if a wizard keeps using spells, they will drain their life force until they either can't even move any more, or they die from expelling every last bit of their own life. Magic is obviously very powerful, and can cause far more destruction and damage than any sword or arrow. But it's also the most dangerous, because no matter how careful a wizard is, they are putting their life at risk every single time they cast a spell.

As such, if a wizard attempts to cast a spell that's too powerful, they could kill themselves with just that one spell. It's the same as mana, except their mana doesn't regenerate until they rest and if they run out of mana they die. While a fireball may take up a small amount of their life energy, trying to summon a spirit to fight for the wizard could be very, very costly and either put them completely out of commission for the rest of the battle, or even kill them. It's like having a battery. 

So the point of it really is that magic use is far more limited than other combat styles in how often they can actually attack. They have to be careful about what attacks they use, how they use them, and most importantly how often. They can't just throw out spell after spell. 

Magic is a double edged sword.

We can be lenient on how people go about doing quests of course. I agree with the general feeling here that if we tried to have one single plot that everyone followed at once, with the amount of interest this has it would be chaos lol. This way, usually people will be out on quests and a smaller group would be left at the guild to socialize and all that. Then we can do major events, and split it into different roles so that we can have different groups do different parts of the same event. It gets done without the chaos of too large of a group, and everyone still gets to be a part of it.