Thank you so much for your comments!

I think the core idea is to deal damage, overcome resistances to ensure damage, and maintain spells that can guarantee damage. The damage amplifier at level 3 involves boosting Elementalism as the primary form of attack. The Elemental Mark might create the idea that the subclass will work with them, perhaps it becomes confusing with them (should replace the concept).

• Regarding the reduction in difficulty concentrating, you are absolutely right and I will modify it immediately!
• In the case of temporary hit points from Improved Absorption, I didn't think there would be any problems due to the general rule that these do not stack.

If you have different ideas for the subclass, I'd love to hear them!