The growths and bases of most of their representatives as well as the fact that they are locked to 2 or 3 range for the vast majority of the game if they want to dish out respectable damage, maybe?
Nah, there is no reason not to love that class.
Being locked to 2-3 range is managable. Other classes have rather suckish 2 range options. Snipers(and the like) have high hit, and plenty of damage with steel. I would hope that you're not soloing chapters with them(although Shinon could), so staying out of a one-ranged enemy's way isn't very hard. The only time that I see this excuse creditable is when you're doing a low turn count run and your other people are locked up doing something else. I see it as being beneficial at times, I would much rather my sniper unit A lure out enemy ranged unit B then I would want my Halberdier unit C with a javelin.
Maybe the reason why I like them so much is because I take this game generally slow, dealing with enemies a few at a time when possible.
(I brace myself for the punch in the face that's coming for suggesting that bow units are useful)
I don't suggest that they are terrible or anything. Even Leo has his good points. Just that Shinon being amazing in 4-E does not equal "epic pwn".
Also their mastery is (skill/2). This is bad, but at least they have a 40 skill cap and +15 crit, so it isn't as bad as it could be. Even Trueblades have a better mastery (if only slightly) because it is effectively 5x damage instead of 3x damage. The difference doesn't matter very often, though. And anything with skill% or str% or spd% is obviously going to be a better mastery. Calling Deadeye an awesome mastery displays a lack of understanding of game mechanics. They have a "mediocre mastery" at best.
Astra takes five uses of a weapon (If you use five hits.) Deadeye only uses one hit, so it balences out. Besides, Mastery Skills are pretty much one hit kills anyway, so why does it matter? (Except for bane...)
Still, one range is over rated. >>
Wispers fail. (<3 Heather & Sothe)