I feel ES has been trying really hard to walk away from the features Solr is good at. While ES still supports multiple languages and custom tokenization chains and even custom pre-processing chains (somewhat equivalent to Solr's UpdateRequestProcessors), I felt that they were very deeply buried in the configuration, when I look at ES a year ago.
ES is truly focusing on metrics and things and does have some features to make those use cases easier that Solr would probably need a lot of configuration/customization for.
So, Solr is about search. ES is about a specific set of use cases that rely very heavily on search.
And Lucidworks Fusion (commercial alternative to ES) is about big data and ML and full multi-tool pipeline on top of Solr.
ES wins hands down in search in my experience because the companies that were doing search stuff "before it was cool" were mostly running stuff like Autonomy DRE which work well but are expensive and proprietary.
There is a huge market just by going after that kind of customers.
ES is truly focusing on metrics and things and does have some features to make those use cases easier that Solr would probably need a lot of configuration/customization for.
So, Solr is about search. ES is about a specific set of use cases that rely very heavily on search.
And Lucidworks Fusion (commercial alternative to ES) is about big data and ML and full multi-tool pipeline on top of Solr.