This is true for backend frameworks too. In the PHP world, Laravel contains many helper functions that uselessly duplicate functionality already available in the standard library. Not only is this a waste of effort from the framework's author, it also unhelpfully silos some developers into Laravel-specific knowledge. I had a colleague who had worked professionally as a Laravel developer for several years but then failed a job interview because he'd literally never written a vanilla PHP script and had no idea how to go about it.