No, that part of the code is correct – the Engine is designed to run inside other software, not just Akeeba Backup for Joomla!. The plugin needs to push the directory to the joomla25 platform implementation to the Engine:
Platform::addPlatform('joomla25', JPATH_COMPONENT_ADMINISTRATOR . '/platform/joomla25');
This populates the static variable \Akeeba'Engine\Platform::$knownPlatformsDirectories, therefore the if-block you are referring to does not load. This is what we're already doing in dispatcher.php in the front-end and back-end.
You were very close, but thank you for the heads up! I know where to look now. The next version will include the bug fix.
Nicholas K. Dionysopoulos
Lead Developer and Director
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