Office 365 Groups and Categorize emails

I disagree. You can't point to a single feature enabled in one product and say that every other product on the market should offer an equivalent. That's not the way that things work. And any reasonable assessment of what G Suite offers in terms of functionalty will conclude that Office 365 has more.  (My view on the matter is at https://www.petri.com/battle-cloud-supremacy).

Customers can't behave like babies and stamp their feet and say "we want" either. That's no way to exploit the potential of software. Instead, after they make a decision as to what cloud application suite to use (hopefully Office 365), they need to understand the capabilities of what's available and decide what makes sense for them to use in the context of their business requirements. There is seldom a 100% perfect fit, so some compromise is necessary. Heat from management might highlight an issue, but it won't solve it. Nor will it make software change to create new functionality.

The Office 365 Groups roadmap has a lot of new features coming in the relatively near future (see the Ignite sessions for details). Some of those features (like soft-delete) are absolutely more important than shared access to a group mailbox through Outlook desktop, especially when a perfectly reasonable alternative (regular shared mailboxes) exists.

All software follows a development plan. Features in that plan are weighted against other demands in order of importance. My perspective (and feel free to disagree) is that what you're looking for is relatively low importance when compared to other features, like making sure that the hybrid experience for groups is more seamless than it is now. You can lobby for the feature you want... But you'd probably be better off understanding the full breadth of collaborative capabilities that exist within Office 365 so that you can guide customers to make the right choice for their needs. In fact, it seems like Outlook desktop is the point of unification here as both shared mailboxes and groups are resources accessible through the same client.

What you can also point to is the dramatic evolution of Office 365 Groups since their introduction two years ago. Groups have come a long way. More needs to be done and will be done, if not when and how some people expect that to happen.