IMHO, the history was different. Java applets were initially secure in a sandbox and faster than what was possible with the "javascript" of that era.
Applets have become slow to start many years latter when bloated "enterprise" applications have been produced in abusive ways.
The security of applets has started to deteriorate a bit slightly before the death of Sun. It has become a security hell only since it is in the hands of Oracle.
The startup time was horrible. The speed, once it was running, was good, but the startup time made it completely unusable on the web. The ugly default UIs in Java did not help.
I did my fair share of applets back in the day, starting with the very first public versions and have very vivid memories of the loading screen :)
You should also take into account that internet speeds of that era were not as great. Today, we download multiple megabytes of javascript. Back then downloading the same multiple megabytes of java was slow because of network.
I always wonder -- if Sun had forced people to build their own loading screen UI per applet -- how the perception of Java (and Java Applets) would be different.
I recall loading webpages in IE where the browser would completely stop for 30 seconds while the JVM fired up.
JavaScript at the time was mainly used for snow flakes on the web page or annoying mouse trails on the web page, as I recall. Oh, and maybe rollovers. I remember Microsoft pushing DHTML and seeing IE4 as a leap forward compared to IE3 but I do recall Java being slow. And slow.
Applets have become slow to start many years latter when bloated "enterprise" applications have been produced in abusive ways.
The security of applets has started to deteriorate a bit slightly before the death of Sun. It has become a security hell only since it is in the hands of Oracle.