I like the idea of a monster bestiary. Its definitely something that would be fun to fill out, and feels very final fantasy ish. (I know some FF's have done it, don't recall exactly which ones) But imo they still need the option for aggro/linking/level displayed on mobs. The option to turn off aggro icons (and i'm assuming linking if they incorporate it into the aggro icon) is going to be on a toggle, so no need to kill it for everyone and not give the player a choice to use it or not.

I'm not sure if you have a problem with level indicator as well though, really its not different than the color indicator we currently have (aside from giving exact amounts to some ranges) unless you had a problem with being able to know what level you could fight a mob at any given time as well. But adding a monster bestiary on top of what we're getting is a plus to me so hit the like button for that.