Size isn't necessarily Power or Strength.
We tend to instinctively equate power with size. We assume that the bigger, more muscular person is objectively stronger - but that's not true.
100% with you on that one. This why i've been saying from the start that there shouldn't be a modifier on weight based on Str.
Real life swordsmen are actually pretty strong though. They aren't big, which is what we usually think of when we envision "muscular". But, talk to any fencer and they'll tell you, successfully pulling off moves with the necessary speed requires significant strength. Hands, forearms, upper arm, shoulders, chest and back for weapon positioning; hips, abs, and legs for thrusting and movement. Fencers have scary strong hands and forearms. They remind me of the grip old dairy farmers have (from manual milking).
Exactly. A fencer in the game with a Str of 16 could look like an average guy size-wise.
Yet the paradox remains for this specific fencer can lift 460 lb. above his head and cover 5' per round at a stagger, as frankthedm has pointed out.
In the real world, muscle coordination, speed, and strength are intimately interconnected. Look at sprinters today. In the past it was always assumed that strength training would just bulk you up and was counterproductive to speed - turns it out that's not correct.
Actually this IS correct... in a different cense... I don't think the example of the sprinter is very good one... but let me explain.
A sprinter does not differ much from the bodybuilder/powerlifter type. The both work their muscles very hard for a short period of time.
Sure, a sprinter is super fast, ...alas for 100 meters, in a straight line, on a flat surface, and for less than 10 seconds.
A powerlifter, does this exact same thing with weights. He can lift 400lbs a couple of times in a row, and then he'll rest.
But when judging the speed of a person i think it's appropriate that we see this from a different perspective.
The sprinter runs in a straight line, and his body and muscles are "locked" in a given position. Outside of that, his size and big muscles will work against him. The lack of flexibility will prove to be an actual flaw if we compare him to... say with a parkour runner.
In a multitude of environments and time limits/frames the sprinter is useless, when compared to builds able for a wider range of "speed" feats.
We are all aware that in races, the bigger the distance, the less bulky and muscular the competitors are... Going to the extreme opposite of the 100m sprinter is the marathon runner... obviously a "skinny" athlete.
...Sure we now begin treading in the territory of Constitution D&D-wise, but despite that, can we say that a marathon runner lucks "Strength" when compared to the sprinter?
Is the Sprinter "faster" than the marathon racer?
Strength has many faces, and i believe that in D&D it is better to embrace all those types under the single Str score.
The more we do that the more it makes cense how Str makes 50% of the attack roll.
And what if my 16str fence can lift 460 pounds overhead and walk with it?
Personally, I can live with that paradox better, than imagining that my 16str fencer is Arnie with a rapier and a dagger.