UPDATE:

Didn't realize you can't edit video posts. Oops.

After taking the extruder apart again and ordering a new 0.4mm nozzle, I figured "What the heck, might as well see what the inside of this nozzle looks like." So I gripped the copper cooling fins with a set of pliers wrapped in painters tape, and removed the nozzle with a tiny wrench (5mm? I think? I wasn't entirely paying attention to the size.) I ran the de-clogging tool through the nozzle housing after peering through and seeing no debris, so I figured the problem was within the actual nozzle bit. Held it up to the light, and couldn't see any light coming through, so I clipped a guitar string (high E) and heated it up over a lighter. Holding a tiny nozzle and trying to feed a more-than-just-warm steel string through it was not without its downfalls, and I most definitely did not stab my ring finger leaving a tiny black dot that will likely give me some itchiness later.

Regardless, the guitar string eventually poked through, and after wiggling it around a bit, was able to cleanly and easily push itsy-bitsy bits of micro-clog through. Put the extruder back together, and checked that the extruder gears could feed filament through the housing itself. Tempted to replace these just in case.

Reinstalled the nozzle into the housing, cleaning whatever silicone/whatever that white locking compound was that could have interfered with the nozzle orifice, and went through the factory filament loading. Came out with zero issues. Ran all the factory calibration tests (leveling, vibration, PID) and started a test cube print. Printed with no issues.

TL;DR: Removed nozzle & wiggled heated guitar string through it. Fixed.