This is @#$%^ frustrating. I often perform assessments for my clients, where I check the existing Teams/SharePoint site setup, security, info architecture, and other settings. I click on Group/Site Permissions, see 10 users being part of a group, and… all 10 are Group Owners. Let me explain why this is a bad idea and can lead to inadvertent intellectual property loss.
Group Owner is not the same as Content Owner
You might want to read this post I wrote a few years ago. Though you own a car, it does not mean you know how to drive it. Same with SharePoint Sites/Teams, being a group owner means you understand the consequences of it: how to configure its security, site sharing settings, or, in the context of Teams, its Group Settings.
Group Owner means you can delete a site
As I documented in this post – Site Owners or Group Owners are pretty dangerous people. Group Owners can delete the whole Office 365 Group (Team, Site, Calendar, Planner, etc.). Yep, the entire thing, just like that. Yes, you have a grace period during which you can restore it, but do you really want to get that point?
One-two Owners per site is all you need
While it is always good to have a minimum of one Group/Site Owner for each site, you do not need more than one-two. I like to say that you should always give the users the minimum security level they need to do the job. On some sites, it might be read-only access, with group sites, it would be Member (Edit) permission level. If I were to ask you for the last 4 digits of your credit card number, would you give me all 16?