Hi,
Thanks for your reply. At the end of the day it is your plugin, so you are free to do what you wish.
Just to address a couple of your points:
> 1) The link is added using javascript and is not crawled by google
I am an experienced SEO professional and I can confirm this information is false. Google has crawled and indexed javascript content for many years now, by default. To see what is rendered you have to use the Fetch as Google tool, not view page source.
> 3) Showing a “Powered By” link a common practice among a lot of SaaS providers including OptinMonster and Privy.
Totally up to you as the plugin developer of course, but personally this is exact reason why I would NOT install a service. The plugin would have to provide a huge benefit to justify this.