Just a general question: I am just wondering, why every tutorial for child themes still includes the parent's stylesheet. Would it not be preferable to de-enqueue & to de-register the parent's stylesheet and then just to copy the parent's stylesheet rules right into the child theme's
This way, you would have one less page request on load and you'd also be able to change css rules directly without overwriting them by using child's css rules with a higher specification. If you are going to change the design in a fundamental way, you could save many kB's (and maybe repaints? I don't know).
Of course, I also see the downgrade aswell. If the author updates the theme with css changes, you will probably face abnormality in your design, because the updated parent's stylesheet will not be loaded. You then would have to target the css changes and apply them to your stylesheet.
But all in all I think, this could be worth it in regards to performance or am I totally wrong and am I overseeing some fundamental aspects?