And that downshifting involves a clutch operation, moving the engine into a higher RPM. That most certainly wears down the clutch, talking as someone who's replaced quite a few of them.

I've seen an interesting A-B test with this seeing the difference in clutch wear between the Ferrari F1 transmission in the 599 and 612 and the DuoSelect transmission which is essentially the same box in the Quattroporte. The shifting strategy and technique is more of a controlled variable here because the shifting is automatic though it's a somewhat traditional manual gearbox with hydraulic actuation. The QP is a bit heavier but the Ferraris make a lot more power. From what I saw the cars that fared far worse were the Quattroportes, and those that ate the most clutches by far were the ones putting around the city, especially in San Francisco, Marin, Los Altos Hills, etc. where people are slowly creeping into parking spots on hills. On the Ferraris that are weekend warriors that get driven hard the clutches could go 30k+ miles no problem, Quattroportes would come in with smoked clutches in a few thousand miles sometimes.

I didn't quite get if you think changing gears for the purpose of engine braking wears the clutch more than normal or not. Are you using the force from the clutch to force the engine to go from a low RPM to a high RPM? In cases like that where the difference in RPM is significant, I would press the clutch pedal, then speed up the engine by pressing the gas pedal, downshift, then release the clutch. Rev matching, basically. It does wear the clutch a teeny tiny bit, but not more than any other gear change.

If your comment wasn't meant to imply that engine braking wears the clutch more than normal gearing, if you just want to avoid gear changes as much as possible, disregard this comment. (Although... I'm not sure that that's a valid worry, modern clutches last a LONG time when used properly)

Are you really shifting so much that your clutch slip in the middle of the shift effects clutch lifetime?

Clutch wear occurs when the clutch is slipping so you always want to minimize the slipping time.

My 300k km Volvo S60 still runs on its original clutch, and I changed the brake pads only once. Engine braking is the way.

Most of clutch wear comes from making it slip, while accelerating from a standstill.

You don't make it slip when shifting gear.

The clutch wear on a standard downshift must absolutely negligible when compared to accelerating from a full stop and especially when compared to slower-that-idle operation, i.e. parking.

Also, I have never ever had to replace a clutch, and I drive my cars way past 100k miles.

Yes but actually no.

It wears the clutch but clutch wear is massively dominated by starts from a stop or other cases where you actively slip it any noteworthy amount so just rowing the gears up and down doesn't do much.

It's a negligible amount, especially if you (or your car) does rev matching. My last car (BMW 328) made it to 300k miles on the original clutch.