It is true though that you are paying a premium for marginal gains, but that's how it is in any hobby or even just about anything in life that as you want to attain more, you'll have to deal with diminishing returns.
Personally, it is a company's (both Motul and Liqui Moly) reputation is what got me sold - they are both very long established, and both very actively involved in Motorsports.
Liqui Moly is even the official Moto2 Moto3 lubricant.
Then, there's base oil. Motul more on ester and LM on PAO.
AMSOIL generally group 3 then mixing PAO/Ester (if any, they don't advertise a lot)
There's also recent API /SAE recent studies on LSPI, and AMSOIL overdosing calcium could be a concern for high performance/direct Injection vehicles.
I truly doubt Motul or LM are better in the real world than Amsoil despite having better base oil. Maybe you can try then do oil analysis test to compare with your favorite Motul and LM.
This post has been edited by 6UE5T: Jun 29 2019, 11:47 PM