I can only give you my opinion.
If someone copies an idea of yours and builds something similar I don't think it's a big sin.
In human history there are countless more or less fraudulent episodes of plagiarism.
If you register the rights of a song\software to the relevant authorities, you can be pretty sure that whoever copies your work
it can then be prosecuted. I say "pretty sure" because governments have sometimes just got hold of private patents
making the previously registered patent "disappear" by replacing it with theirs.
In your \ our specific case, since you do not have the possibility to register a patent, you are not protected by anything \ anyone.
Indeed I will tell you more, the provider that hosts your intellectual property (practically free of charge) could without giving you any reason
take over your work.
But I don't think that big G uses these means, given the stable of programmers at their disposal :-)
If anything, I'd rather believe that Google contacts for a job interview than a genius programmer discovers in his Store.
We're always talking about extensions and not the Star Trek warp engine.
I don't want to sound numb, but as great as your extensions are, I don't think they can ever change the world.
But if you think you had the billion dollar idea, then use other channels to monetize it and look for a good lawyer to protect your interest.
But perhaps there would be a way to protect our labors.
We know that Google doesn't want us to obscure our code (because it wants to protect its users and itself),
However, Big G could make our already approved source code unreadable with JS obfuscation techniques
or by transforming the JS itself into a pseudo-machine language interpreted only by the browser.
In this way the danger of copy \ paste plagiarism would be averted.
On the user's side, however, the ability to debug the extension would be lost in case of problems.