I completely agree with the idea that ES might be good as a distributed search index. I really wish people would leave it at that.
The company where I last worked had a main product which would send in readings every second. The only interface to these readings was Elasticsearch. dev-mis-ops were convinced that this was a good idea. Even the front end would send its queries to Elasticsearch to display statistics.
My task was to look at the average energy usage over one year for the seven days in the week divided into fifteen-minute intervals. This is literally just a SELECT MOD GROUP BY in SQL. I am not even talking about more advanced SQL features here like windows, transactions, joins and so on.
I tried for ages looking through terrible documentation trying to get it to work, at which point I thought I’d have one of the resident ES experts take a bit of his own medicine. It took about five attempts of back and forth over two days to get it right.
This wasn’t the only query we had problems with. At some point, I just asked them to give me a CSV interface so I could do it in AWK. You can’t even download CSVs of data sets without some external tool! They were still convinced that ES was fit for purpose.