Block is pretty pointless because with full armor and magic resist you already have a fully passive ability to resist 80-85% of all damage, with no need to melee, activating anything or investing 9 perks. If failed to achieve that, then obviously block will appear to be useful for protection.
Why don't you try the skill before commenting on it? I've got full armor, 50% magic resist, and a ton of elemental resist on top, and while I'm not taking
much damage, I do take damage all the same. I can't let a dual-wielding briarheart go to work on me for all that long before I run low on health, despite the 85% damage reduction. I can block every single one of his swings, though. In fact, I did that to take block from mid seventies to 100. Took maybe ten minutes or so, while I was reading the news and simply holding down my right mouse button.
Also, you don't invest 9 perks in block solely for protection. To that effect you only need shield wall 1, deflect arrows, quick reflexes, elemental protection, and block runner. Five perks. Then you add shield charge, shield bash and maybe deadly bash and disarming bash for offense.
Finally, unless you're using a two-handed weapon then what else would you be carrying in that off hand? Anything that could even begin to match up against shield charge?
Weapon power attacks stun too. If its one mage, he is as good as dead. If its a group of mages, then for every interrupt done, the other mages throw firebolts at the player. Essentially it is an exchange of 1 firebolt(of the targeted guy) for multiple firebolts the other guys fires in that time. Pretty bad trade off!
Shield charge, is all I'm saying. Just sprint around in a circle and all the mages will be on their asses. Then hit one of them a few times, run another sprint around the room, and so on. Works great unless there's a frost mage around, since the cold slows your sprint.
Contrast this with the alternatives. What could you do with that left hand that would be inherently more efficient than holding a shield with, say, +50% resistance to two elements, a further +50% resistance to fire, shock, frost when blocking, always staggers when used for bashing, sends targets flying when sprinting. That's a pretty solid list of features, isn't it?