I have been wondering if there is a feature or any 3rd party tool which could help me creating a report to visualize not just the distinct count closed deals of a team but also the average per person linked to that team. (Number of deals / count of team members)
You can add external content to a HubSpot Dashboard, yes. If you create a simple Google Looker Studio Report with the data from funnel.io, you can embed that into the HubSpot report.
there is currently no option to make calculations like that in the HubSpot report builder.
You could get there with 3rd party tools though. A combination of funnel.io and Google Looker Studio can get you there. Funnel.io has a free plan, so I think this should be possible without any additional cost.
You can add external content to a HubSpot Dashboard, yes. If you create a simple Google Looker Studio Report with the data from funnel.io, you can embed that into the HubSpot report.