None of those sound easily hand waved. No offense to the makers of DnD or any of those other games, but that sounds like they were running short on creativity, and I would be quite disappointed if any of them were used. If casting a force hammer exhausted a forcemaster like that, she would not have the strength to swing her galvitar for 8+ dice of damage multiple times after that.
Having Arena rules like that be the thematic explanation too for a life and death match just doesn't work. Priestess pays triple book points for dark spells. Do you really think that's just because the referee said so?
Having spell memorization be so difficult would actually justify bringing a spellbook into the arena. However, it would not justify having spells actually disappear from the book or become unreadable after a certain number of casts, nor does it thematically justify the spellbook not taking up the shield or weapon equipment slot.
I think a fully trained mage would know what spells they want to cast when they want to cast them and be able to fight on the fly like in Harry Potter and wouldn't keep having to reeducate themselves about the spells they know mid-battle by reading a book that they wrote themselves. Mage Wars is a very dynamic and often fast paced game, and the styles of the mages very greatly. I think having to read while you're fighting for your life only thematically works if you take a quick action to do it, since reading takes at least some time no matter how highly skilled one is in magic.
I don't think even the priest would take his holy spellbook into battle with him. To tarnish a book of prayers like that with bloodstains would be sacrilege to Asyra who Malakai serves. If he reads from his spellbook, it would be before the fight.
Spellbooks should be for learning or relearning spells, or because they have some powerful magical properties that make them useful as an equipment.
For instance, I imagine that the first libro mortos belonged to a legendary Necromancer, perhaps the very first one, and all the other libro mortos cast spells that were in the original. That way, the reason the undead obey a Necromancer is because they mindlessly follow after the first Necromancer that controlled them and his descendants, and they don't see the difference between that Necromancer and the current ones because they're zombies and skeletons.
From what I understand, mages generally can only prepare two spells per round because they can't keep more than two spells in their working memory at a time, which is an idea strongly evidenced by the existence and function of mordok's spellbook. The only other explanation that I can imagine anyone giving for that would be that each mage has two hands and therefore can cast two spells in a round. However, that is debunked by the fact that the spells are not cast simultaneously and do not even temporarily take up any of the hand equipment slots, weapon, shield or gloves.
This suggests to me that a mages arsenal of spells are in their head, rather than in a book. Otherwise they'd probably be able to prepare as many level 1 spells as they wanted per round because they would be taking the time to read them in their spellbook and level 1 spells are simpler and easier to memorize and recall.
I think that the power of magically imbued words is the most logical intuitive explanation, since otherwise, why would mages use words when casting spells at all? Would incantations exist at all?
It might sound silly in real life, but considering that the major schools of magic, the six main kinds of magic that are studied in Etheria have human values inherent to them, I don't think it's that far off to say that words can have that kind of power too in Etheria.
Also, thank you for bringing the huge thematic inconsistency about spellbooks to my attention and to the attention of anyone else who reads this thread. However, for future reference, threads on this forum are killed after 60 days and it is against the rules to reanimate them. While I don't approve of your having necroed the thread since that's against the rules, I think what you said was valuable insight and needed to be shared. Since you have already reanimated the thread and gotten it bumped onto the unread thread/thread reply lists, I feel like it is too late to counter your spell so to speak. Though you probably shouldn't cast it again.