The autoload.php file is currently not optimized for the case of a pure LS stack installed via composer.
It would be a good idea to describe the best settings (speed-wise) in config.php-RECOMMENDED, while at the same time lowering the visibility/priority of the configurations

• including the bundled zetacomponents
• using zetacomponents somewhere else

As far as I can tell, the best way to set up autoload in such a case is:

define( 'EZCBASE_ENABLED', false );
ini_set( 'include_path', '.' );
require_once( _DIR_ . '/vendor/autoload.php' );

While for the case of a non-pure-LS, the best config.php (creating it by itself removes one uncached stat() call) is currently:

define( 'EZP_USE_BUNDLED_COMPONENTS', false );