The whitelist mode could explain the lower number of connections.
"3.0.0 - requires user token if instance is in whitelist mode"https://docs.joinmastodon.org/methods/instance/
Sidenote: activity endpoint sounds like a great addition.
vis.social is an open social platform for creative people, especially anyone in SciArt, SciComm, data, visualization, creative coding, and related arts and research. English is the common language of the instance.