As for why not just level up to mid-class Magus and be done with it?
This is really redundant, because the skill points required for Kain to upgrade to [★★] equivalent to mid-class is too terrifying, that is why Kain has to take a detour.
Don't think that collecting 80 skill points is easy because he earned them. To do that, he literally hollowed out a floor.
And that number of skill points is nothing compared to the number of 1000 skill points, it takes at least 12 to 13 times that 80 skill points to collect enough.
But the number of skill points Kain had collected from the beginning until now was not even half of that.
So, instead of digging for 1000 skill points in vain, where there is a high chance that after upgrading, there will only be a bunch of skills of unusable level 0 magic. Kain chose to optimize his strength, in order to lay the foundation for collecting skill points later.
And he feels he's on the right track.
