I understand that, but being able to forego a shield/faith spell, or wear head/cloak/rings that provide something else is a boon, not a drawback.
I like an FE weapon more than a simple deflection AC vs. enemy type weapon though, for sure - it's more versatile and of course MHs need that.
But, with that said, now that you mention it, I was thinking of it like favored enemy and was confused. Is it just because of how MH interacts with FE that it gets to use Studied Foe? Do they have to rest to 'enable' the feat, like turning classes do for extra turning items? Either way, that's a lot better than having to hold it out for combat.
edit: This is kind of a tangent but I just feel weird about studied foe in general. I really just think it's so strange that it lasts such a short time. They do all this in-depth study, seeking forbidden lore, probably performing their scholarly training in a ritualistic way (given this class is not a mundane one), to the point of gaining a prestige class, and they get this buff that is very short-lived. It seems cheap to give MHs a "free" extra studied foe by acquiring these books. But then, it lasts such a short time anyway, that it can hardly be called the class's main feature. If it lasted a really long time I would understand, taking a glance at a book with a one-round action to gain the benefit would be kind of cheap. If only it worked like spells where using it off the book meant you had the shorter duration and using your main Studied Foe was better.