You don't need much space to add a backdoor to a plugin.
The increased jar size is mostly due to the fact that we use Kotlin now, and we are bundling the Kotlin standard libraries, so you don't need any extra dependencies to use the plugin.
You can see it yourself if you open the plugin with an archive manager:
https://imgur.com/WKPQ2td
Also, the plugin is not obfuscated, you can check the sources on GitHub and build it yourself.