It is a centuries old cliché:
Inept commanders prepare to re-fight the last war, rather than equip to win the next war.
Your "amphibious landing craft" & "privately armed individuals" imagery addresses an infantry style invasion, literal boots on the ground.
Possible.
EXTREMELY unlikely, as you suggest.
The U.S. is ALREADY at cyber-war, Stuxnet being a mere primer.
In 2014, Sony Pictures suffered a devastating and highly publicized cyberattack related to its planned release of the controversial film The Interview, which intelligence reports later attributed to a nation-state attacker.
France's supermarket refrigerators were recently hacked.
Oct 12, 2026 ... Hundreds of French supermarkets have been hit by a cyber attack that caused their fridges and freezers to heat up, spoiling fresh and frozen ...
Hundreds of stores were targeted by the overnight hack, which spoiled fresh and frozen food estimated to be worth millions of euros.
www.bbc.com
French fridges not the end of the American world, BUT !
this well publicized attack in France demonstrates U.S. vulnerabilities.
In conclusion:
We agree the type of threat you describe, which we are well defended against, is exceedingly unlikely.
In contrast the type of threat more likely to extinguish U.S. may be over, the U.S. may have lost, before most Americans became aware it had begun.
Whether that's a total nuclear volley launched at 3:AM so the mushrooms have sprouted before dawn,
or an alternate scenario such as a bio-engineered pathogen the enemy attacker has vaccinated its population against, causing a plague from which the U.S. never recovers ...
Superb.
But the Hegseth / Musk / DOGE / Trump meat-axe approach is not surgery, it's butchery.
None of these clowns understands as much about U.S. national defense as the senior U.S. military commanders they've fired.