Java never ran well on the desktop or in the browser (arguably it never truly ran in the browser at all), and it was an extremely low-productivity language in general in that era.
There is a significant gain from running a single language everywhere. Not enough to completely overwhelm everything else - using two good languages will still beat one bad language - but all else being equal, using a single language will do a lot better.
Yes, Java was never really good (I'd argue on any platform. Server side is fine, but not "really good" IMHO)
It made me think about the amount of work that went into JS to make it the powerhouse it is today.
Even in the browser, we're only able to do all these crazy things because of herculian efforts from Google, Apple and Firefox to optimize every corner and build runtimes that have basically the same complexity as the OS they run on, to the point we got Chrome OS as a side product.
From that POV, we could probably take any language, pour that much effort into it and make it a more than decently performing platform. Java could have been that, if we really wanted it hard enough. There just was no incentive to do so for any of the bigger players outside of Sun and Oracle.
> all else being equal, using a single language will do a lot better.
Yes, there will be specific cases where a dedicated server stack is more of a liability. I still haven't found many, tbh. In the most extreme cases, people will turn to platforms like Firebase, and throw money at the pb to completely abstract the server side.