So I would assume Delvac1 failed from your own oil preference?
In this particular case, the oil didn't meet my expectations for a 5k km analysis. It may be specific to my engine so i can't say that the oil is bad in general. Price also played a part, it's too expensive to change every 5k kms.

Isn't that a good sign that the oil viscosity is higher than what it should be? Better engine parts protection.
Typically, it's not normal for an oil to exceed a certain viscosity increase. It should stay within a 25% range of orig spec within the drain interval. Oil thickening is caused by either base oil breakdown (burnt oil) or high soot build up (more than what the oil filter can handle).

A degraded base oil won't have enough protection while a highly sooted oil may cause increased wear metals. Think the best protection is from properly spec'd oil, doing what it was designed for.