Grease on pedal threads just collects grit and makes a mess, dry threads have always held torque better for me. A little anti-seize is all you need, not full on grease.

1/16 on oak is asking for it, but I don't buy that a test pass on scrap would've saved you here. Scrap pine cuts totally different than solid oak, so a test run tells you almost nothing about how the real board will grab. What actually bites people is grain direction and feed speed, not the depth number alone. Running 1/16 in shallow passes at a slow steady feed is how most guys flatten big slabs, and it works fine when the knives are sharp and you don't stop mid cut. Sounds more like the planer caught a climb cut on reversed grain than a setup shortcut.

Two parts riding the top limit out of 400 isn't a crash, that's just normal tool wear on the last few pieces. Six inserts across two shifts at 120% on 4140 sounds about right actually, that's not "burned for nothing" money. If the load meter never blinked and your mic checks out, the setup guy has a point. I'd run 4140 around 110 to 115% and save the 120 for aluminum where the inserts can take it, but I wouldn't lose sleep over this run.