When you view a web page it evaluates the scripts and renders the result. You’re currently retrieving the page info and then would need to do the same.
You might be able to parse the content and then evaluate the script and run it on the page, but if there’s any server interaction that would become significantly more complex and even as it stands it would probably be rather difficult and tied solely to that page so if it changed it would break the algorithm used.
I don’t know of a way Scriptable could effectively pose as a browser, internally render the page and return the resulting content in some format - definitely one @simonbs would be best placed to answer.
Would another option be if you were to view the page in a browser yourself and then pass selected content into Scriptable? I know Shortcuts can retrieve evaluated web page content from Safari via the share sheet, so at worst you could use that and then pass on the content to Scriptable for further processing.
Hope something in there is useful