The state of configuration

[liayn (Markus Klein)]

@crell

define a Configuration/TCA/Overrides/<tablename>.php file. This file is loaded if and only if the corresponding table is defined elsewhere

That’s incorrect. It simply loads every file in this folder. The naming schema is only a convention.
$finder = Finder::create()->files()->sortByName()->depth(0)->name('*.php')->in($package->getPackagePath() . 'Configuration/TCA/Overrides');

Moreover, the whole TCA is cached, see \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::loadBaseTca. So your statement about the various TCA files being loaded on every request is not quite true.