Is it? Or a wasted skill?

Of course it's perfectly viable!

Because I have my weapon in the other hand...

Therefore all you need to give up to wield magic is your shield.

Hammering the heck out of everyone with destruction magic - and if they get too close - boom!

One shot from my double-enchanted Stalhrim war axe equals toast.

I'll trade the shield for magic any day...

And I can of course even create a magic shield (if I wish).

I don't like two-hand magic at all.

1h destruction + 1h mace is a badass combo.

Destruction also works pretty well with a shield in the other hand.

I'm not sure if it's a question of viability as much as it is a question of redundancy. Using a weapon in one hand and casting destruction spells with the other is totally viable (and pretty fun) but it's kind of a half measure. Why not dual wield and really put the hurt on the baddies? Why not dual-cast and get some serious pop into your destruction spells?

My limited experience with spell-swords was an exercise in using destruction magic for a ranged attack and then melee weapons up close to finish off the baddies. The downside was never having quite enough magicka or health or stamina as compared to a dedicated mage/fighter. With a dedicated build, you can really build the primary attribute, gradually increase the secondary attribute and forget about whatever is left for third.

Yep, that's why I suggested shield. Even with no armor, you can block a lot of damage with just a shield, plus the slow time block perk would combine nicely with a flames/frostbite/sparks spell. Plus you can stagger with the bash. Unlike wards which eats up your magic like nobody's business, a shield costs nothing to use, so it goes perfectly with a magicka hungry destruction build. Also, I am pretty sure that a shield does not mess up your mage armor perks, if you wanted to use them.

Very viable. One of my favorite "types" is the "spellsword," with a weapon in the right hand and a variety of spells in the left. You can even use Destruction as your ranged attack, instead of a bow, if you want.

I'm currently playing a "spellsword" who uses Destruction, 1-Handed, and Restoration. One favorite tactic is to set a rune trap, then cast a fireball or lightning bolt to draw the enemy to the trap. She'll switch to a healing spell if the fight is going long.

It's a different fighting technique, because you can't block.

Dual-casting doesn't get you that much more attack for the magicka expense. You can do a lot more damage over time with a combination of an enchanted weapon and a supporting spell. Use the runes and cloaks to advantage, and weaken the opponent, while using a high-damage weapon.

True- but you need Dual-Casting to get Impact. Once you have Impact, you're in fat city.

I suppose. But you're getting 10% more destruction by using 40% more Magicka, so I wonder if the Impact is really worth it. I've played a number of mages, and I don't think I have never taken the Impact perk. But then again, most of my mages get more use out of Conjuration and Illusion (where dual-casting can actually be necessary.)

In any case, the question was whether one-handed casting is viable, and it certainly is.

Viable? Absolutely.

Fun? Well... It's subjective. Destruction got a downgrade in spell variety this time around.