I think it's pretty clear that there are both kinds of power users: the ones who take pride in being able to learn whatever defaults there are, and the ones who take pride in being able to customize the defaults to their preference.

I don't believe either group is any more right than the other: both sides have about equal amounts of good arguments and pointless posturing. A tabs-vs-spaces situation. Fortunately, in this case, we more often than not have a choice: computing environment GUIs are still pretty personal, so everyone can just use software that follows their expectations. The problem begins when a user from one side is somehow forced to use software following the other side's ideology - but that's a separate story, and arguably it's the "being forced" part that's the actual problem.

Personally, I'm very inconsistent in this regard. There are apps that I've been customizing for more than a decade and, quite honestly, I wouldn't know how to use them were my config to suddenly stop working (Emacs, ZSH, tmux). On the other hand, there are apps I've been using for a similarly long time, but never bothered to configure (other than possibly installing a bunch of plugins): Firefox and Vim come to mind.

There are also apps that I do customize, but either only once and never touch the config again (my window manager, Awesome), or ones that I customize but only to add an escape hatch (adding "Open this file in Emacs" to all JetBrains IDEs, for example).

So from my perspective, what's essential is to have a choice: both GNOME and KDE should exist, should enjoy similar popularity, and should each focus on their favored philosophy. Let those who want to work with defaults use software where a lot of effort went into providing sane defaults (it's ok if customizability suffers), and let those who want to customize use software where significant effort went into allowing customizability (it's ok if defaults are slightly insane).