I've had multiple config bankruptcies over the years until settling down with Doom. I'm considered "experienced Emacsian" - built and published packages, etc. I'm still using Doom but only the core of it. I don't even consume almost any of its "official" modules - I have my custom ones instead. I have considered building my own config from scratch (yet again), but I like Doom's core macros - map!, add-hook!, defadvice!, undefadvice!, etc. I'd probably inevitably end up borrowing them and structuring my new config just like I already have, so I see no point.

> I don't fully understand the editor

Going vanilla will not help you there - well, not completely anyway. Moreover, it may even obscure some features that were easily accesible before.

> I don't fully appreciate the difference between what comes in as part of vanilla Emacs and as a Doom feature

That is not very difficult - learn how to use built-in features - profiler, edebug, describe-, apropos-, hooks and advising, etc.; Start writing Elisp code (with understanding it). In the end, it won't really matter - whatever runs in your Emacs, there's always a way to get to the source. And if you ever need to disable any feature of Doom - there are multiple ways to do that.