You're telling me they go through all the trouble of rolling out Teams so it connects to Office365 groups, rolling out PowerApps for Teams so that apps can be viewed right there in Teams (whether desktop, web, or mobile), have it all connect to information in a SharePoint (information OWNED by an O365 group, I might add), guiding us to using SharePoint and Office365 more, but I cannot even share access to an Office365 group? What numbskull is running this show?
And while your "alternative solution" works, you have to realize how ridiculous this is. We create O365 groups where all the data, the messages, the SharePoint access, ALL that jazz is managed under one group, including integration with PowerApps, except you have to create a Security Group that mirrors your O365 group. That's nice, except there's no way at all for you to tell the Security Group to mirror the O365 group, because that's not a possibility in Dynamic Security Groups. Another ball dropped by Microsoft. When is M$oft going to stop failing halfway through a project?