Everything you said is true, and I’ll add onto that. From a durability perspective, anything machined from billet steel is going to be exponentially stronger than the same part made from stamped sheetmetal.
However, an AK is more than just a receiver, it’s an assembly of components intended to be used in a myriad of unimaginable environments. A small amount of flexibility in the receiver could be beneficial if the rifle were laterally stressed (ie the rifle were sat on, dropped, or if the operator fell on it while
in a sling, etc.)
A solid receiver would transfer lateral stress to the barrel, and raise hell.
An AK with a tweaked stamped receiver, but intact forward trunnion and barrel, will still shoot straight.
So why do I want a milled AK? Mainly because I don’t have one yet, and they look nicer. I’m a big dude who likes the extra weight not because recoil bothers me, but because a heavy weapon doesn’t jump around as much with repeat shots.
But if we ever had to bug out, the first rifle grab would be this frankenstein AK I built from commie surplus parts that has never skipped once and still shoots straight with irons ten years later.
Edit-
oh yeah.... meme