The Liberty ships were little more than motorized barges, with an expected lifespan of about 5 years. Comparing their tonnage to modern shipbuilding is silly.
No it's the entire point. I'm illustrating how US WW2 shipbuilding is pretty mid relative to modern shipbuilding, and that US, on paper should be able to exceed their WW2 output.
Currently JP, roughly pop size of US during WW2, is out producing peak US WW2 ship building in gross tonnage. They are known for building small/medium size higher value hulls closer to WW2 size. Modern shipbuilding during PEACE TIME with a competent workforce and industrial commitment, is capable of producing more GT of hulls with more complexity than US whole of society mobilization during WW2. Of course modern surface combatants are very complex, but USN force design 2045 is all about distributed lethality on less complex hulls + attritable autonomy. Lots of room for 5-10 year lifespan sensor/missile boats.
They proved durable enough for the high seas (something you generally can't say about barges) and many made multiple crossings of the oceans and plenty went on to live typical lengths of service in commercial use afterwards.
