Aimeos is much more lightweight. The Aimeos Laravel headless ecommerce platform only contains around 1/5th of the code of the Magento core for roughly the same feature set. In addition, the optimized data structures make Aimeos extremely fast. You can achieve a render time down to 20ms for cached components without the problems of a full page cache as used by Magento.
It also scales much better than Magento. Magento works fine up to 50k products but will get slower and slower with more products. Contrary to Magento, Aimeos can utilize Elasticsearch or Solr as drop-in replacement for storing and/or searching/filtering products. Thus, building Laravel headless eCommerce applications with 1,000,000,000+ products is possible without any performance loss by using the #gigacommerce extension.
Moreover, Laravel is currently the best PHP framework. It's much easier to use than the old Zend framework Magento is based on and developers are more productive when using Laravel. There's also a lot of documentation and videos available for Laravel and it has a very big developer community.