I think main difference between todays and WWII production is higher quality stantards.
Workers require more and customers wants high quality.
Meanwhile products are also more complicated.
You could basically build a P51 in a small workshop, while you need a factory filled up with precision tools to build F16.
Back then people didn't either pay so much attention to structucal stress or flaws in metal.
Heck.. you could've belly landed in a plane and it could been brought back to service few months after.
Also spare parts were scavenged from planes which weren't worth repairing.
Like one B17 was built up of two different B17's - one had front section totalled and the other tail section -> hey, let's combine intact sections of the two planes!
Made a good mix.. you see the other was olive drab and the another unpainted aluminium
Of course soviet union is a grand example of low quality & high production output.
It's amazing what you can do when you care less about the quality.