Interesting discussion, but as always on a forum type situation, there is a preponderance of classroom or theoretical evidence and ideas. Then the actual users chime in with "real life." And you end up with a theory versus reality/practicality deadlock.
In real life cruising most things and boat systems evolve primarily towards practicality rather than the theoretical optimum. Taking some of the points in the last few pages . . .
All chain rode on a one anchor boat is most practical primarily for wear, abuse and fouling (where long-term anchoring
is involved). The bottom of a lot of harbors and bays/coves is littered with all manner of debris ranging from sunken boats, to construction debris (cement blocks, metal beams, and other sharp edged stuff). Add in nature's coral
heads and small reefs
and you can see that hardened steel
survives better than nylon.
In some harbors, pollution is rampant enough to foster massive sealife fouling of anchor rodes and cleaning
it off nylon rope rapidly shortens the usable life of the rode.
For boats with dual anchors rigged on the bow then one of each works very well. All chain on your heavy primary anchor and then rope with a 30ft to 50ft chain leader on the other anchor. Usually one anchor is chosen for weight like the classic CQR
or Bruce and the "other" anchor for soft sand/mud capability (historically a blade anchor such as Danforth/Fortress).
Again for practicality, in short duration anchoring where you are moving from one place to another daily or every few days - and - the sea bottom is sand/grass/mud, the blade type on rope rode makes life simpler both on windlass
wear and if necessary, hand hauling of the anchor & rode.
But for long term (weeks or more) anchoring the all chain rode is more practical for the reasons already mentioned.
As to using "heavier than theoretically needed" chain again it is partly a practical decision. Steel
chains lose their galvanized coating quite quickly in today's "acid" oceans/rivers/bays. Then the chain starts to rust and getting progressively smaller - especially where the links are rubbing against each other. The heavier the chain, the longer life you get.
As to large ships using heavy chain and rather less effective anchors, there is a historical reason that you would only know if you were involved in the industry. Typically large heavy ships deployed quite a length of chain upon entering a harbor and "dragged" it all the way in until they were docked. The dragging anchor/chain was their speed brake and aid in turning their vessel to align with the docks. Also it was later used to kedge the ship's bow off the docks when it was time to leave. Having an effective anchor on the end would have prevented such a use.