An error occurred while saving the commentBetty Stolwyk commented
This appears to have been corrected. I gave this another go with the most current Teams Client Web UI and all is well. I created a new Team and verified that it built an associated SharePoint site, an O365 Group (visible in Outlook from the Group drop-down and visible in Azure Active Directory Groups), and Exchange Group mailbox.
After verifying that all the expected objects had also been created, I proceeded to delete the Team through the Team client Web UI. (right-click Team name, and select Delete from drop-down menu)
A warning dialog box popped up (nice!): Are you sure you want to delete the team "xxxxx"? All channels, chats, files, and the Office 365 Group for this team will be deleted".
I checked the "I understand that everything will be deleted" checkbox, then clicked the "Delete Team" button.
Going back I verified that all associated objects had been deleted : SharePoint site, the O365 Group (no longer visible in Outlook from the Group drop-down nor in Azure Active Directory Groups), and Exchange Group mailbox.