We are at ArcGIS server version 10.5.1 and statistics still are not supported. First, why are they not supported? Second, is support at least on the roadmap?
This effectively eliminates the use of query layers in the new version of operations dashboard. If you try to create a category filter for instance, it executes a statistics query before retrieving distinct values!
outStatistics on a query layer is supported in 10.3.1.
pls see 'New in 10.3.1' section in ArcGIS REST API - Map Server Layer Resources help topic.
if it does not work for some reason, pls contact Esri Support and it can be looked at.
Retrieving data ...