The trouble is that they ‘enqueue_block_assets’ is not the right hook to use for conditional resources anyway. The correct hook to use for the backend is :
add_editor_style( 'path/to/my-core-style-overrides.css'),
which should be inside 'after_setup_theme'
hook.
This will ensure that these styles are incorporated in the admin editor iframe only and in all places where that iframe can exists such as when editing the theme via wp_enqueue_style
hook. This hook can now be contained in wp_enqueue_scripts
to ensure it is frontend only.
A bit of a mess I know but a correct implementation.
The original reason for this question was due to a plugin I wrote for conditionally adding resources to a post or page. Whilst this can be done it will not function correctly on the backend anyway without a page reload every time a resource is added. Therefore all resources should be added to the backend and conditional resources added conditionally using login on the front end.