We can confirm, Kibana 7.4 is faster than Kibana 7.9.2.
7.4 is using "_msearch"
7.9 is using async search, which is horrible (in our case).
We setup a 7.4 cluster, reindex data from our 7.9 cluster, re-recreate Kibana stuff, then load page. Kibana 7.4 dashboard is loading 10x faster.
Is is possible to disable the new async search?