If I only give the title of the book it terribly hallucinates, and Kindle doesn't make it easy to copy book content into clipboard :/
So then... removing DRM would be the most direct way to accomplish that. It's DRM preventing you from doing that, so removing the DRM is the way to fix that. Much like removing CSS to rip a DVD.
If you prefer, you can also look for already-pirated copies on the torrents, Anna's Archive, libgen, etc. But the cleanest copies would typically come from such de-DRM processes anyway, unless they somehow got a copy of the pre-DRM originals.
"Hacky" would be more like using a script to turn every page of the Kindle book and then using OCR to rip it page by page and some ML to reflow it into a good layout. Or scraping the Kindle/"See inside this book" preview pages or Google Books previews one image at a time and feeding those to an AI API one chunk at a time.
By contrast, removing the DRM from the file you already have and ending up with the exact same file minus the DRM... that sounds way less hacky (and way more reliable!).
And Calibre can help with transforming the source format into something else (plaintext, PDF, or HTML) for easier parsing.