What do you think, all the rod bearings were out of spec in the rods, bearings, or crank?
OP do you have any plastigage? You could put some of the bad parts back together and see where it's at in the unaffected areas if there are any.
I don't know what to think, not experienced enough, the only thing I know is that all the engines we bought from two very reputable engine builders had stock tolerances assembled with new parts and we only ever used 10W30 per their request. I don't buy the 5W20 thing when the same Ford told customers outside the US (who can get any oil they want, as we did back then) to use 30 oil instead. When you got a new mustang in latin america, the original manual said 5W30 instead of 5W20 (I can scan it for you if you want).Also, local Ford, always serviced 3Vs in F-150/Explorer and mustang with Motorcraft blend 5W30. And finally, 5.4 4V engines use the same clearance spec of the 3V in rod/main bearing to crank and comes with 5W50.
I've never used in a customer car or mine 5W20, never.
But as I said, I am not experienced enough. So, only my .02.
Probably a 10W was not good in current weather? maybe, I don't know.
What I think is that if mains are good, don't think it was an oil issue.
Looks rods are toast now so don't how effective would it be to measure them. I would get boss rods or manley turn the crankshaft and plastigauge them at install and sort them.