Misunderstood then, though I'm coincidentally still debating the same topic.
We would've had loads more diversity if they'd bothered to make two-handed, one-handed and sword/mace/axe completely different, but they didn't. Two-handed and one-handed play almost exactly the same, as do sword/mace/axe.
As to your specific point, yes and no. In many cases, you'll be able to cast a spell beforehand, THEN switch to your sword and board for the fight. Even the diversity of shield vs destruction magic is debateable, as one ends up feeling ridiculously superior to the other. To me, diversity also demands that there's SOME logical reason to use a different combination, not just that you CAN use it but one of the options is stupid as hell in comparison to the others.
I'll certainly agree that the dual-wielding mechanic could have been implemented in a better manner, and that TES has lost a few things along the way from Arena to Skyrim.
It's also added a few things.
There is certainly potential in Skyrim's system, what they do with it is anyone's guess. I was personally expecting some bonus for using certain equipment and/or spells in tandem, but alas... we will have to see what VI holds in store.
Just simply trying to say that there are potentially just as many builds available, if not more, when considering 4 things :
Dual wielding
Shouts
Ability to use any skill/spell, with no restrictions other than time invested.
Perks
Now the amount of skills and spells, thats not really debatable... TES has dropped a few of those without adding enough to replace. Its a net loss in my book.