Yes, that part is intentional. For one, as has been said, killing is easier than most other things. Instant effects can create powerful permanent consequences, but they have two advantages: a) you can't control them beyond the instant and b) the consequences are non-magical.
To compare two examples: You can incapacitate someone by breaking his legs (instant effect) or by paralyzing his legs (duration effect). The first is cheaper. But those broken legs can be healed, magically or otherwise, while the paralysis would have to be dispelled or countered with a similar spell that would be at least as expensive.
Also, you can't undo the instant effect, which sucks for blackmailing.
Nevertheless, this is one area where you can "game" within the system by experimenting. Sometimes, an instant effect is better, but sometimes a duration effect will be better, especially during roleplaying.
Duration has been left out for reasons of complexity. The usual distance is "near line-of-sight" meaning that if you see it clearly you can hit it, without the usual problem that "line of sight" extends to the horizon (true, but at that distance you don't really see your target anymore). If you want to cast spells into the remote, a combination with a spell that allows it will be needed.
Finally, don't compare SM3 to D&D. We have two things that make it a very different game. One is that it's about storytelling and the other is that all spells are going through GM control. And in case of doubt, the rule that spells are precise will bite you. With the headache-inducing spell, you simply can not kill someone. It causes a headache, end of story. You can not use spells creatively.