Shared dashboards accumulate charts the way inboxes accumulate mail. The cure is intentional retirement, not another redesign.
Assign an owner to every board. Require a written primary question for each chart. If nobody can answer that question in a standup, archive the chart.
Separate operational monitoring from exploratory analysis. Ops boards stay stable; experiment boards get an expiry. That separation keeps leadership views trustworthy while analysts still get room to explore.