Regarding deprecated rulesets: I think there was a new feature introduced, which makes actually all deprecated rulesets appear.
As can be seen in that commit (Refactoring: Moved check parameters from unsorted.py to dedicated mod… · tribe29/checkmk@c499319 · GitHub ), already in January 2019 many of the rulesets shown in your screenshot had been deprecated (probably even long before).
Then some where already deprecated in 2.1 (e.g. local checks in Checkmk clusters, Inline-SNMP, check for correct version of Checkmk agent, piggybacked Docker containers), which can be more easily seen when looking at 2.1.
The, some are counted double because they appear under service monitoring rules and enforced services.
So the number is more like <10 deprecated rulesets.
Can you please clarify why this is surprising? It is rather normal, if features are deprecated, e.g. because they are replaced by new features (e.g. we completely rebuild the Kubernetes monitoring in 2.1, which includes many features, which were covered by the Prometheus integration, thus the respective elements were deprecated for the Prometheus integration).