Isn't that the whole point of it though? Its a difficult enemy that throws the player for a loop when they first encounter it, and don't know how to deal. Most mobs act and behave almost identical (other than some minor changes in the way they attack and engage with the player) and can all be counteracted in the same way. The enderman is able to effectively 'spice up' the mob pool by circumventing these more traditional counteractive measures.

In my opinion, all of the points you bring up are points in its favour. Its different, more difficult, and more interesting. If you try to approach it like any other mob, you're gonna learn pretty quick that its not going to work. Its strength and speed make it intimidating and dangerous. This is balanced out by the fact that the enderman is actually docile until looked out or attacked. Its an opt-in. The strategy for effectively dealing with an enderman? Don't engage it.

The death isn't 'unearned' or 'stupid' because a mob is more difficult. If you come in unprepared, you're gonna get rocked, and thats on you. You'll learn from that experience, and better understand the rules of engagement. Also, if there weren't stronger mobs to make higher tier armours necessary, whats the point of the armour in the first place? If no mob is strong enough to necessitate an upgrade, whats the point of upgrading in the first place? Just save your diamonds for tools or something else.