And you have data to prove that Jag got it wrong?

 

Without an oil pressure and possibly an oil temp gauge there is really no way to tell if the oil is still working in tough conditions. I would not switch without first installing these gauges and getting a baseline.

 

A historical review of long term engine reliability and durability while using the two oil viscosities in question shows no indication of any issues.

Applying 1950s-era Chev V8 thinking to modern engines or reading too much BITOG or than for pure amusement is usually a mistake.