I'm sure you've seen the Mobil slides I've posted where they compared their 0W-40 to other approved oils and even their own lower tier oils where the difference in deposit control and prevention are eye opening to say the least.
What it comes down to is whether you want "good enough" or better than that.
An SKS is "good enough" to harvest a deer, but it isn't a very good, or accurate gun. It's cheap, and does the job. A precision rifle at 50-100 yards will be more accurate than the SKS, but does it matter when the SKS is "good enough" and the precision rifle is arguably overkill? But what happens when the conditions change; what happens when you end up needing to make that 200+ yard shot and "minute of barn door" is no longer good enough?
With a rifle, the difference between a $250 gun and a $2,500 gun is pretty easy to determine at the range. With oils, that difference is far more difficult to see, requiring tear-downs and inspections, but that doesn't mean the difference isn't there.
The API approvals don't set the bar very high. GM's dexos spec bumps it up, but the ACEA protocols are more stringent still, then you add the Euro OEM approvals on top of those and you create a situation where the SKS/Amazon Basics might be "recommended for" but isn't approved

That's why I like the layered Euro approvals, as I think that really sets the bar at a reasonable level for performance.