1. Range: You don't use your own judgement, it's just guesswork. You hit the skill and if you're in range it goes off, if not you get an error, move closer and try again. No real skill involved there, just guesswork.
2. AoE: Same as above, except if you're not in range it simply doesn't hit them. No skill involved in guesswork.
3. Enmity: Arguably, knowing what the hate situation is will allow a player to push the limits harder than before when they were simply guessing. Instead of wondering if they're close to pulling hate or not, they know and in knowing they can use that information to play more skillfully.
Even with the aid of various information displays, personal skill is still needed. It doesn't matter how much information you know if you don't know how to use it to your advantage. If you can't do anything with that information, you may as well not even have it. You need to know what you're doing to properly utilize the information that you are given.
Simply knowing the AoE range doesn't help you much if you don't pay attention or know the limitations of certain skills. Also some lesser known bits of info, like AoEs only hit up to 8 things at a time, are not made apparent and must still be learned anyway. The best way to utilize certain AoE skills despite their range is another personal hurdle that some must overcome. Simply knowing where it will hit is only half the issue.
Exactly, also again if a player doesn't know what to do with the information then it is useless. The enmity bar is really only useful if people know how to manage their enmity properly. Seeing red on the bar doesn't help you much if you don't know how to shed hate.
Actually FFXIV is still kind of aimed at a casual audience, more casual than FFXI at least. Things can still be challenging even with information displayed. Knowing something only does so much for you and the rest is up to personal skill/judgement. These things don't make combat inherently easier, they just display information which you must then use yourself. Figuring out the best way to use that information is what keeps it challenging.
That's an awful idea, I'm sorry. Punishing people for using an information display? No, I would not stand for something like that. Those who don't "need" them can be rewarded with a personal sense of superiority or something, don't punish people for using a feature in a game.
Putting an information display in doesn't take up a huge amount of resources. Compared to creating dungeons, quests, gear, etc... it's a pretty small thing. It requires a little testing but all it does is display information, not a lot can go wrong with that compared to other things.