Based on the information brought back by Leon and the others, along with Keoghan's conversations with Lord Sarubo, the Mages quickly determined that this was a small-sized material plane where the highest tier of power was limited at the Fourth Grade.
Magic Elementium was lacking.
Arcanology was incomplete.
The characteristic of magic in the entire plane hindered the casting of spells. This meant that way more effort had to be put in to successfully cast spells. Even so, there was still a rather high chance of the spell failing.
The powerful Elementium manipulators and casters could not maintain their class advantage before the classes that relied mostly on physical damage due to the difficulty of casting. That was why the terrible situation of witcher knights oppressing casters happened on this plane.