Is it normal for my filament feed to stutter on a QIDI Plus 5?

You're not seeing things. That intermittent slow-down and wobble on one of the feed gears is a real thing with these units, and your slow-mo video is exactly how I spotted it on mine after weeks of blaming everything else. I did the same song and dance as you: belts, bed, flow calibration, different spools, and the pulsing surface on PLA stayed. What actually fixed it was adding a thin shim between the motor and the gear assembly so the motor gear stops riding too far out and only catching some teeth.

The way it failed on mine was sneaky because the mesh is fine at one point in the rotation and then loses contact depth on part of the gear, so the gear drags and wobbles for a beat before re-engaging. Watching it at normal speed you'd swear your eyes are lying. Filmed it and it was obvious.

How smooth is supposed to look: with the cover off, run the extruder motor slowly by hand or at low feed rate and the driven gears shoud turn at a perfectly even pace with no change in pitch or speed anywhere in the rotation. If you hear a slight tick or see a hitch once per revolution, that's your culprit. Also grab the driven gear gently and check for axial play, mine had just enough to let the teeth slide out of proper mesh.

For the fix itself I printed a shim and started thin, testing after each thickness change untill the gears ran even all the way round. Took a few iterations because the exact thickness you need will differ from mine, so don't assume someone else's measurement transfers. Some people just file the gear edges where they bind instead, wich is quicker but less reversible. One caution when you take the housing apart: note the orientation of the springs and the little tension arm before removing anything, and don't let the filament sensor parts drop out. Photographing each step saved me a reassembly headache.

Do the slow rotation check first though. If the hitch shows up once per gear revolution you've found it, and no amount of recalibrating will fix a mechanical mesh problem.

I'd push back on the hand rotation check though. Mine looked totally smooth spinning the motor by hand with the cover off, and I nearly moved on because of it. The skip only showed up once I fed filament through under actual load, so the gear was shifting under pressure in a way it doesn't do unloaded. If your slow rotation comes back clean I wouldn't close the book on this. Run a test print and film the gears while it's pushing filament before you order or print any shims. Saved me from pulling the housing apart for nothing.

Something that helped me narrow down which gear was the bad one: put a dot of white paint marker on each gear tooth face and watch where the hitch lines up. If the hitch always happens at the same paint dot, that gear is the problem. If the dot is in a different spot each time, look at the motor side instead. I do printer servicing as part of my day job, maybe 30 units a month through my bench, and this trick saves me pulling the wrong part half the time. Also check the gear for a flat spot on the shaft, an out-of-round gear gives you the exact wobble you're describing.

Seconding the point about the skip only showing under load. Mine spun like glass with the cover off and I nearly talked myself out of the whole theory. The thing that finally sold me was listening with the top cover off during an actual print, I could hear a faint tick once per revolution that matched the pulses in the surface finish. With a fresh spool of a stiffer filament it got louder, so if your hand check comes back clean, run a print with the housing open and just listen.