Hahaha, I'm doing my best to be polite and nice given that somebody is effectively bitching about the code I wrote, that they're using, for free.
You keep whacking on about this admin email being used everywhere. It's not. Deactivate the plugin, all emails come FROM wordpress@yourdomain. This plugin makes no change to the TO address, which is, you guessed it, the admin_email.
I don't think it's a reasonable assumption to say that because somebody installs this plugin, they want the from email address on all emails to automatically be the admin_email. If I understand what you're suggesting correctly, you're saying that should be the default. How, then, would a user choose to have the "default" wordpress@mydomain as the from address? They'd be expected to enter that instead?
In my opinion, the plugin does not change the from address unless the user explicitly asks it to. That seems like a sensible default to me. But like I said, if you feel strongly, by all means, create another plugin. Hell, if you feel strongly enough, I'll hand over admin of this plugin and you can modify it as you see fit.
Bottom line, the plugin works as expected and as described, the fact that you think it *ought* to be different is noted. If it's a request I hear often I'll consider changing the default.
May I do anything else to be of service?
[Disclosure, I'm the plugin author.]