It is still somewhat effective. I have one page on my website that has my email address on it. That email address is unique to that page and I don't use it elsewhere. That page:
Doesn't use a mailto: link (you have to copy and paste the email address from text on the page)
Is disallowed by ...
There is no difference in performance between yarn and npm except during the package installation process(install, update, and remove). For watcher and executions it's depend on script and node JS version, So package managers like NPM and Yarn doesn't affect watchers and executions performance.
Google renders pages and waits for a while before taking a snapshot of the page. Last I checked you had about 5 seconds to render what Google would see.
So I suspect this may not get indexed.
You can test this with the url inspection tool or one of Google's testing tools which will show you the rendered html that they may use. Note that timings in the live ...
Google is concerned with showing the result that matches the query of the user. I think that it's going to be rare that someone searches for a specific line of the lyrics to a song and expects to find the lyrics with chords.
I don't fully know what your site is about, but music, lyrics, and chords gives me enough to say that the following are likely going to ...