I’m
not so sure about that. I wouldn’t say always.
Young America was shown to
develop this strength at an early age because of the abundance of settlers that
propelled his economy forward. However, because he lacked true independence,
was taxed a lot by England and fought wars for the latter, there were times
where America was considerably weakened. His “economy [became] strained.”

Likewise, he had initially lost a lot of battles in the
Revolution before making a comeback. He wasn’t as strong then compared to what
we see depicted of him more in the strips.

Once he became independent, America likely gained this super
strength back + some. You also have to consider how he lost strength again as a
result of the Great Depression.
Nonetheless, he didn’t become a Superpower, which includes
global political and economic dominance until after WW2. A Superpower status
only added to his physical strength, allowing it to grow to unprecedented
levels unlike any other nation but Russia, his rival.
In other words, America’s strength fluctuated as a result of his
economic situation. Now add independence and a Superpower status, and you have
an unprecedented amount of strength.