The following are the pretty straight forward steps I followed to get Alchemy installed on a Tridion 9.1.1966 environment:
WARNING BLURB: As always, take care when modifying your windows registry settings by hand. I would recommend backing up your current registry unless you are completely comfortable with editing it yourself. Remember, you accept any ...
To my knowledge, plugin settings are only available on Controllers and JS Resource files.
Alchemy Controllers are inherited from the class AlchemyApiController and since Plugin property is defined in AlchemyApiController that's why Plugin.Settings only available on the controllers. Other than controllers the plugin settings could be accessed on the JS ...
AFAIK - Alchemy Installer - It is currently not supported in tridion sites 9.0+.
Anwer to your question
Q: Is there any way to install the Alchemy plugin without Alchemy?
A: No, Alchemy plugins wont work without Alchemy framework.
There is a possible hacky way to install Alchemy Installer in Sites 9.0 and 9.1 by your own risk.
The current Alchemy ...