Having run the new Throne of Thunder LFRs without having read, seen or heard about any of the boss fights, I've come to realise that the Dungeon Journal isn't really a journal.
Although it's a good idea - people having a quick skim of boss abilities before entering a fight so that they know approximately what to do - it's neither here nor there. Hardcore raiders would point to sites like Icy Veins for more detailed killing strats; casuals would find reading the descriptions tedious.
In my opinion, to make the Dungeon Journal a proper journal, boss abilities in the Dungeon Journal should update automatically only AFTER you have seen the boss abilities.
ie. If you make it to phase 2 in Onyxia, Onyxia's abilities up until phase 2 are visible.
This way, it won't change anything for people who want to know the fight before going in, because most would look at raiding websites anyway... but it makes the most sense in terms of lore. Plus, it gives a sense of achievement - we made it this far and figured out that the boss does this - it'd be just like keeping an actual journal.
Guilds in previous expansions that went into raids fresh and spent hours through the combat log after a wipe for which spells hit when and for how much etc had the right idea; it's just that for most people doing all of that takes too much time. Why not tie the Journal in with the Lorewalkers and act as a combat logging analyser rather than just a dictionary?
Loot lists are a different story, of course - you could spend an entire year and not see items drop, so having the loot lists available beforehand makes sense.
I know it wouldn't be easy to change the Dungeon Journal system, but still... it's all in the detail!