If you mean in terms of scheduling events, they're pretty much the same. Some functionalities however are not exposed when using PFs or Group mailboxes, for example the option to publish the calendar. Scheduling Skype-based meetings is another example.
(1) We need a company events calendar. Everyony in the company needs to be able to view it. I think i want everyone to be able to add events. Ability to view via Outlook, via browser, and via mobile is needed. Being able to include a lnk to this calendar in Yammer is also important.
(2) Second scenario is a report calendar. It's needed by a group of people that span different departments. Would like for it to be accessible via Outlook and Teams. Would like deadlines to show up in the personal calendar of the party(ies) responsible for completing the report.
(3) A central calendar to display staff member vacations.
This is one area where ExO/O365 falls short. The usual recommendation is to use a PF calendar or Group based one, but they all have some downsides. It's choosing the lesser evil, depending on your specific requirements.
PF based calendars, or shared mailbox ones have a problem with mobile devices. PF ones also cannot be published online. Embedding any type of calendar in a webpage is also a pain (the Publish functionality is what you can use, but it's limited). Group based ones can be accessed via the respective mobile app, but the "equal access" model might cause you troubles there.
In general, if you have some dev resources your best option would be to leverage the APIs and built in your own solution. @Juan Carlos González Martín might be able to give some recommendations to the SPO side of things.