The one from my BITOG moniker - 2012 DL650, Suzuki Wee Strom. A 644cc V-twin with only 67 hp and 41 lb·ft torque, it's not at the ZX14 or Hyabusa level for meting out driveline punishment, so it should get even more mileage before shift quality drops off, all other thing being equal.
Admittedly, I'd like to think your simple explanation of shearing the oil's viscosity index improver in the clutches and gearset provides the explanation, but if it did, wouldn't you expect there to be an obvious marked difference in between the 100°C dynamic viscosity in the VOA and UOA? I think it came out well within spec for all of the non-300V MC oils.
I surmised the cause had something to do with the oil's friction coefficient changing during the oil change interval - like as result of combustion blowby, fuel contamination, or clutch pack material suspended in the oil. As I said in my previous post, a fresh oil change always perfectly resolved the problem, until it got enough mileage to gradually start coming back. But a change of 300V stayed great for the whole time it was in the crankcase, including well beyond the manufacturer's recommended 3500 mile OCI. So I stuck with it.
My current bike (2020 GSX-S1000F) is still breaking in at ~ 5k miles, so I'm still using a mineral MC oil to get to maybe 8 - 10k before switching over. This one seems to begin losing shift quality at ~1800 - 2000 miles on the Motul 3000 10W40 MC oil that's in it now.
There's no need to think someone's favorite is the solution to every problem. If your were one of the chemists or blenders at Exxon-Mobil that came up with the formula for their 4T, I can see why you'd have something invested in it. If someone else came here and said they tried my suggestion of 300V (for street or off-road riding, read: not racing) and only got 2000 miles before the shift quality went south, I would 100% agree it was a waste of their $20+ per quart and they should try something else. The majority of us here are just riders and occasional mechanics, and the best we can do is learn from our experiences and honestly relate what we've learned.