No Doubt! Shields were used because they worked! Seriously, to be more realistic, shields should have bonuses more akin to wearing Plate.
Yeah, that's been one of those carry-over mistakes that D&D has kept around. Back during AD&D or earlier (IIRC) it was noted that weapon weights included the scabard, baldric, etc. - not just the weapon (at least that's what I was always told when I started playing AD&D 2E - but I don't have those books anymore to find the reference). The weapon weights have carried over through 3E. 3.5E, and 4E mostly unchanged, but the note that the weight includes these things didn't make the trip.
In my stick fighting days as a teenager, I was the only one who had a shield (made of an aluminum disc sled). Comparitively speaking, I never got hit. I even held off 2 other fighters. From my guesstimate, with actual swords and actual shields and actual skilled sword fighting, I'd rather have a shield than nothing.
In my 2E days, scabbards were sold seperately in the PH. I suspect weapons had inflated weights (just as they do in videogames) as some sort of atttempt at game balance through inventory space costs.
On the 10lb sword thing, i was exagerating. But the point is, for an experienced big man who is swinging his favorite big weapon, the weight is trivial because they've got the muscles and practice to make it so.
Ignoring polearms, versus an immoble target, it should be pretty obvious that a bigger weapon does more physicial damage. The weight and leverage that can be applied makes it easier to pierce, slash and smash the target.
Polearms are wierd, because the interesting part is on the end of the stick. Once you are past that, the weapon's value is limited. Wheras, even a big sword is useful when you're closer in (but not hugging me yet).
The stereotype of big lumbering guy with a big lumbering weapon is to illustrate some point that the little guy can win. A smart fighter doesn't over-extend himself. Thus, he never takes such a swing that he cannot recover to protect himself from a counter move. By not over-extending himself, the big guy with a big weapon will still deal more powerful blows than the little guy with the little weapon.
I'm sure there's some boundary, where the weapon is too big for the wielder, and at that point it would be less effective (the lumbering effect). But a properly designed weapon, even the larger weapons tends to scale up.