From what I understand, yes. Let’s take you through it.

Basically, I believe that
America and Russia’s super humanness stems from a historical allusion to their
status as world Superpowers during the Cold War.

The rule in the series is
that a nation’s strength derives from the strength of their economy, the
stability of their government, and whether or not they hold a dominant position
in global politics. Since both Russia and America emerged as the two leading
powers following the end of World War 2, they achieved a Superpower status. The
logic, then, is that they would be physically stronger than the other
nations. Yes, they were stronger than usual beforehand, but this accelerated their abilities even more.

You even see Finland during
the 2010 Christmas Event referring to America and Russia as super humans.
Again, I think this is a reference to the Cold War, as the power balances in
the world have long shifted since their time spent as unmitigated Superpowers.

Also
important to note here is that Finland mentions that the nations normally are
not that much different than humans. This is
consistent with the rule that a nation is more resilient than a human (aside
from their obvious immortality), but that they still nonetheless need to be a
powerful figure themself in comparison to the other nations if they’re to
possess this additional strength.

I believe that Russia doesn’t
possess his super strength anymore mainly because he’s no longer a Superpower.
He’s still stronger than most, as Finland said, but I think it’s suggested that
his super strength has waned in this strip.

When asked about their current relations, Russia responds by
stating that he used to want to “squeeze” and “snap” America.

He then goes on a sidetracked tangent about how America always
makes friends with people first. More importantly is that after showing annoyance at
Russians stereotypically being made into villains in Hollywood, he admits that
he still wants to smash America’s glasses into “ten equal parts.”

The scene ends with Russia
quickly changing the subject and proving that his relationship with America nevertheless isn’t all that bad. To me, that seems that likewise to his country’s loss of a Superpower status, Russia doesn’t have the same strength to fight America than he used to. Meanwhile, America still remains as a powerhouse today.

That said, for transparency’s sake, I really want to stress that
Russia and America still get along really well despite irking each other and
bearing old grudges.

Lastly, while acquiring a Superpower status allows younger nations
to possess additional super strength, this doesn’t seem to be the case with the older
nations. Like humans, the nations’ bodies age, albeit gradually.

This especially applies to
China and Japan. Japan held the title of the world’s second largest economy,
but if you pay close attention in the strips, a consistent theme with him is
that he’s grown weaker from old age. Ex: He has high

blood pressure, can’t do
strenuous exercise, and is referred to as an old man. 

Likewise, you have the same
situation with China, who’s even older than Japan and is also referred to as an
old man/grandpa. Currently, China would be considered a superpower, and figures
suggest that they’ll eventually surpass the US economy. However, because
China’s body has aged considerably, even if he’s a Superpower, his physical
body may not be able to gain back this strength again.