Cast water walking on them as they are falling off a cliff?
Plenty of skills provide no method of killing stuff (Speechcraft, anyone?). That's why you use more than one.
Magically making a weapon appear for you to use would be redundant in more than one tree. Even shield spells in both would be redundant if they were too similar in how they work.
But if set up properly, speechraft can be used to finish quests through talking instead of killing. Everything and anything could be used in combat. Different ends may be reached through the different means, but at the end of the day each skill has a way to get the job done...except alteration.
All the combat skills can kill. Destruction kills. Restoration can fortify skills to allow you to be better at killing, or talking if need be. Conjuration kills. Illusion can allow you to bypass killing or allow your enemies to kill each other off. Crafting can make armor and weapons, and then make them better at what they do for fighting. Enchanting makes things even better at killing through magic, or allows you to talk better. Alchemy allows you to make poisons. Pickpocketing can let you kill through poison. Sneak allows you to kill quietly. Speechcraft can let you talk your way out of situations but still finish quests. And the two armor skills allow you to protect yourself better/move faster.
The only thing in the same boat as alteration is lockpicking, and I'd also like to see that skill involve making traps.
There's nothing redundant in being able to summon two different kinds of swords. There are multiple types of real swords. Katana's, longswords, and so on. Magic could very well be the same.