Regarding a EXP toggle, I don't mind this option, but you should also be aware that your sovereign level has a huge impact on faction prestige, which in turns affect overall empire growth. The latest changes (slowing down leveling) has resulted in also slowing down empire growth. I have a more indept explanation on that aspect here: https://forums.elementalgame.com/424125
So before adding this toggle, they'd also need to do something that tweaks that as well. Or perhaps just chalk it up as part of the experience the player wants and just make sure the AI can handle it appropriately.
Regarding magic, I do think magic spells are costing too little. With some basic mana reduction setup on your hero (Path of the Mage, Affection, and Mantle of Oceans), you can cast the cheaper spells for 1 or 2 mana. Meaning you can cast them pretty much forever in tactical. My most used spells is slow and haste. Slow, when used on big bad bosses (and with a few water shards) allows me to kill them before they even move. 100x more effective than firedart if you have some troops with you. Haste just makes things even more unfair. Both of those spells cost 1 mana per cast with the aforementioned mana reduction setup.
I also use enchantment spells a lot, mainly city enchantments, I only use unit enchantments when I really need to (and that's not often).