Except that the Focus of Mystery slann can completely shut down an opposing spell caster with no chance for them to stop it. The End Time spell for High Magic is horrendous.
Focus of Mistery will gran you the ability to re-roll High Magic which is most needed now when ubber lords run the battlefield carrying uber ítems. Trading one spell to acquire a new entire lore & End Time spell, by also regaining the forgotten spell is a nice exploit of the rules that no one can complain. Since if you have Access to a lore you gain all the spells + if lvl3 an additional one. You will be acquiring access to new lores, if you cast some cheap spells trading it for most needed lores will see you not losing any spell (cuz you have access to all of them) and already gaining 8 new spells. So Focus of Mistery is still better option (the rerolls are big). And the arcane ítem will be power scroll, for sure. Cast on 10+ a non dispellable game changing spell is kinda awesome. seems like you can shutdown the enemy caster with easy just using 3 dice for secure it, and do whatever you want. Also with the new rules of magic (not a máximum of 12 PD), its seems like a good combination to kill your own saurus warriors casting a purple sun through them in order to get free PD.
When 8th first came out, I was ridiculed for running a 40 strong zombie block an inch in front of my lvl 4 Vamp with death. It did not take long for people to cry, bitch and moan when you start generating 12-24 dice a turn. Then thinking oh well, he can only do it once..... mmm no, every turn. It was really brutal when using TK and VC together, because old TK book allowed old Vamps to cast anything they wanted on them (let alone old Vamps being able to replenish any unit in the game that was considered a friendly/neutral ally, literally any unit) Purple Sun is ridiculous.