That last part (about denying access) at least can be fixed: If scripts are disabled (or if the features needed are unimplemented in the browser), or if scripts are enabled but an error occurs when trying to activate the web workers or whatever other features it might use, then it can display a link to the documentation and you can enter the response manually (perhaps copying from an external program (which can even be on a different computer), which if it is native code might be faster than the web page). (If you can have some sort of protocol identification attribute, then this substitution can be done automatically.)

It is true that it can still be annoying for extra CPU work though (and may waste energy), and if they both disabled scripts/workers and also won't or can't do otherwise despite that it will still be denied access.