I'm the OP, and though I got several great answers from you guys, I feel like adding the following points.
Tool does not improve sense of aesthetics, but may improve result
One important and useful (and obvious) statement is that a better tool does not improve the designer's sense of aesthetics.
However, that does not mean in itself that the designer will produce as good a design with one tool as with another.
When struggling with technical challenges, one gets overexcited with even overcoming those, and fails to be critical of the actual quality of the design of the end result
I experienced this a few times. I struggle with some technical challenges like making
div elements in HTML flow correctly, and this can take a really long time for me, both with trial and error and with reading tutorials. When I finally succeed, I feel proud and feel like I did a fantastic job. I feel my design is fantastic. Until I get back to it in a few days or weeks and realize that it doesn't really have the feel I want.
I suspected, that if I could do the same thing in WYSIWYG, my focus would be on the aesthetics themselves, instead of having my focus simply on overcoming obstacles, and I would have a more "correct" perception of my work.
It seems like from your answers, that this is not an issue for you guys, but I just wanted to clarify what I suspected here.
Time efficiency, goes a longer way, and allows trying more variations
I suspect that people work faster in WYSIWYG. This obviously means that if only fx 15 hours is allocated for the design, the designer can make a better design in that timespan. But even if there is unlimited time, like in some hobby projects, the designer can try out many more variations before getting tired and losing the enthusiasm.