Actually they could make it a quest to get the Book to equip as arcanist (To initially unlock the class, since it is U/U), and you can not equip higher level books because /drumroll please... They all REQUIRE a higher level to equip...so in essence you NEED to do the quest to obtain the book to unlock arcanist (and that quest could be 20...30...40...50...WHATEVER level they decide to make it...)
So the armoury system doesn't necessarily mean you can get the class without any epic event...as you can see it can be quite epic.

PS. Marauder is the only guild in LL at the moment...but if you remember, not only is there an arcanist guild there, but there is also the musketeer guild there (in the Coral Tower, on the north side of LL)