It's great Groups have become an integral part of so many different pieces of Office 365, but the fact that there are so many different ways to interact with groups from different locations makes it rather confusing. I'd like to start switching some of our distribution groups over to O365 Groups, but I will need to put together a small training to introduce users to the concept. I know that I don't want to present groups as something that 'you could get to it here, or there, or this other way, or . . . ", or that you have to go to groups a completely different way depending on which part of groups you want to use. That will confuse people, and makes it harder to see the benefit of Groups tying everything together. I already get enough questions from my boss about why Groups are better than just having a distribution list, and a sharepoint site, and a file share.
So how do others present Groups to users for the first time? And when your users are working in Groups, what interface do they most commonly use?
Show your boss how a new member to a Group/Team gets immediate historical access to all prior conversations, and then show them what you'd have to do to replicate that using an old school DL. Take a stab at quantifying how much time that will save in bringing a new joiner up to speed if they can look backwards and get a look at what has been going on, the culture of that team, etc. This usually generates enough of a lightbulb moment to sell it.
I think you need to differentiate between OWA and Outlook; apologies if my naming convention is off but these UI are very different. IMHO OWA is the most functional but I prefer Outlook because it is the only UI that brings multiple accounts, sites, realms, subscriptions, tenants (and other names I can't remember) into one place.
The majority of my current Groups is through Outlook on the Web but newer Groups for me are more commonly based through Teams. A great power of Groups is to be adaptable by business scenario and also how people like to work.