TYPO3 Core

Yes, this is correct.

I can confim this. If you add images via the image button in RTE the images ( RTEmagicC_* ) are also saved in Website root and not in ./uploads.

If you add the image via RTE and activate the rte html source view, you see src="http://{domain}/./RTEmagicC_dfsdf" in the image tag. The "uploads" is missing.
I also debugged function TYPO3\CMS\Core\Html\RteHtmlParser::TS_images_db and it seems that in the following snippet also $magicFolderPath does not contain the "uploads" path.

if ($magicFolder instanceof \TYPO3\CMS\Core\Resource\Folder) {
    $magicFolderPath = $magicFolder->getPublicUrl();
    $pathPre = $magicFolderPath . 'RTEmagicC_';
    if (\TYPO3\CMS\Core\Utility\GeneralUtility::isFirstPartOfStr($path, $pathPre)) {

I can confirm this. If you insert an image in the RTE you get an error because the magic images are saved to the webroot directory which is usually not writeable. In regular content you can help yourself using the Text & Images element. For content of extensions which only use an RTE for the bodytext (like tt_news) it's a show stopper. There you can't insert images. Disabling the magic images by

RTE.default.buttons.image.options.removeItems = magic