The disadvantages of Magic

It is fact that heavy armor can protect you well, however wearing a lot of armor, or very heavy armor you will get a penalty to your damage output with magic. In the case your numbers of misfiring your spell will be increased.
Magic does have its disadvantages as well. Expect for the start spells, most of the spells in Darkfall need a reagent or component to cast with.
Compared with arrows, it is much easier to dodge spells because spells can be easier found and its travel speed through the air is much more slower. Magic also has a tendency to fizzle more when you are wearing heavier armor, but there is an armor magic casting skill that helps offset it a little if you are able to skill it up.