Metronic by default includes all available plugins for demo purposes. You can remove unused plugins and recompile the bundle assets via gulp or webpack to optimize the bundle size.
We use the bundle method for the best performance and quicker page loading its better to include all core plugins at once within a single bundle rather than loading each plugin separately within different HTTP requests. The bundle file is loaded once and all subsequences loads are taken from the user browser cache.
Also, you can enable server-side gzip for your page assets which will increase the page loading speed dramatically.
To reduce the bundle size and remove unused plugins please refer to this post.
You can check our devs site's Google Page Test Score that's built with Metronic. The score is quite high as can be seen in the reports.