The fact that resistance is essential is just as obvious to me as it is to you :)
However, when playing on a small map, where everything is decided within 20-40 days, it's quite difficult to max out five full resistance skills... If only we could choose the desired skill ourselves, it would be much better. As it is, you often get random skills, and sometimes you have to choose between skills that are completely useless for the current build :( The only skill that consistently appears is Combat, and there's no reason to complain about that. But instead of resistance, you often get melee or ranged skills, which are usually completely useless for a mage.