The guy who wrote the most lines of JVM code ever( Prof. Odersky) , who wrote the compiler that became the first javac compiler, who added generics to java5, himself moved away from java to create scala. Once you use something like scala or even kotlin,you never wanna go back- you realize java world is just playing catchup, They are now like a cola company advertising diet cola is healthy. The functional part of java is not really functional ( allows immutability). They just are trying to survive ,and are trying to add all kind of features to java, just to play catch up. I heard they are planning to add pattern matching in the latest version.
The guys who make some excuse, like kotlin or scala is hard, can really be compared to an older car mechanic saying tesla is BS because their knowledge will become obsolete if it takes off. If you really think a language is hard , you are not supposed to be in the programming business. Also these same guys just use java to program the web. Heck, java is fast but the cost of lost developer productivity in waiting for compilation cant be justified cant be justified for the saved 100 millisecond of processing time. What matters on the internet is the perceived speed and the page load time, and there are so many other ways to achieve that. Like simply upgrading to http2. Or preloading html , js and then “hydrating” the page. The entire source code of the forum dev.to is opensource and you can visit the website to see how fast it is. And its not written in java. This is just an example. Facebooks wasnt written/ hosted on the “enterprise” java. While java is fast and is suited for low latency data processing ( like trading system, or big data), I hate that even with the love it receives, 98% of the so-called java guys just use it for web programming. - Also scala beats java at the thing java does best- fast processing. Ever heard big data processing with spArk.