I do not get hung up on brands. I care about performance and specifications. No brand loyalty here. If Amsoil stops making good oil, I値l stop using them.
Different purposed oils have different demands and requirements put in them. Hydraulic oils need consistent viscosity, temperature resistance, low compressability, and lubricity, amount a few other things. I think most suppliers do a pretty good job of this. Especially given the price point compared to motor oils.
Diesels motor oils have a unique challenge in that they must be able to suspend a high degree of contaminants, such as soot and egr gasses that get passed the rings. Diesel oil must suspend these and remain stable or else you get oxidation and sludge. In fact, when it reaches its tipping point, the particles can drop out of suspension almost instantly causing the oil to go from fluid to sludge within a few minutes. This causes catastrophic engine failure. This has happened to a number of Mercedes Diesel engines in cars, SUVs, and Sprinters where the wrong grade of oil was used. Amsoil diesel oil seems to do a good job of preventing sludging and remaining stable for long oil change intervals, which I verified for myself with oil analysis on multiple brands at regular intervals between oil changes. I can safely say that so long as your engine has a good volume of oil (10+ litres or quarts) the Amsoil diesel oil is good up to 20,000kms or 12,000 miles.
With UTF even some of the cheap oils are good for well over 600 hrs, therefore any decent synthetic will give you exceptional protection for 400 hrs change intervals.
. . . Just my two cents.