Recently, I went to a teaching workshop that I thought was going to be horrible. Then, the guy giving the workshop opened with the question: "Why can a bear take your head off?" coupled with him acting out a head-removing swipe on a student in the front row. I was instantaneously more focused than I had been in months.
This is relevant to football, I promise.
You see, people think that bears are stronger than humans because they are so big, but that is only partially true. Bears also have a lot of built in skeletal leverage, too.
Every joint is a lever. Let's take the elbow as an example because it is a pretty simple joint:
The joint itself is the "fulcrum" of the lever (think the middle of a see saw). We'll call the distance between the fulcrum and the point where the biceps tendon attaches to the forearm the "effort arm" of the lever (the blue section). The distance between the biceps tendon and the weight or "load" is called the "load arm" of the lever. As you can see above, on humans, the effort arm (blue) is much much shorter than the load arm (purple).
Because of the short effort arm and the long load arm, a lot of force (huge biceps muscle) is required to move a relatively small load.
Now let's take a look at a bear's arm:
The effort arm (blue) is a lot longer and the load arm (purple) is a lot shorter versus the human arm.
This means that if a bear and a human had the same size biceps, the bear would be able to lift a much heavier load (or swipe your head clean off your body).
Ok, so how does this apply to football?
Not all humans' tendons attach in the same place. Some people's tendons attach closer to the elbow (making for a shorter effort arm) and others attach further from the elbow (making for a longer effort arm). Even if that tendon is a fraction of an inch different between two players it can make for a big difference in strength--and this occurs all over the body, not just with the biceps.
So even if two humans have biceps (or any muscles, for that matter) that are exactly the same size, one can be much, MUCH stronger than the other. Because of several factors, including a players' skeletal leverage, scouts can't determine a player's strength or speed based purely on their size or weight.
While scouts might drool over the imposing size of a lineman or might look for players of a certain size to play a certain position, size always takes a back seat to talent. Height and size are one of many, many measureables a scout will look at when evaluating a player, and most (if not all) of those measurables are trumped by film evaluation.
A player's dimensions or proportions don't necessarily tell us much of anything about a player in terms of their raw physical skills, let alone their skills as a football player.