Distribution list vs file storage

We're having a bit of a disagreement within our company, wanted to get some feedback.

On one hand, a higher-up became frustrated when he went looking for a file related to a client, and found 3-4 different Sharepoint sites with the client's name.  This was usually the result of different departments creating their own Teams/Sharepoints for the same client.  His feeling is every client should only have a single Sharepoint.  Also, it should be attached to Teams so that Teams users can easily stay in Teams to access the files.

On the other hand, the IT department wants to create Teams (which will inevitably have a Sharepoint) for distribution lists, as it will allow for more modern technology to be used when compared to using traditional distribution lists.  But then that causes problems with the above, as it will result in more confusion about where a file might be located.  

The single email that comes with the Team/Sharepoint isn't really usable because both Creative and Customer Service are storing files there, but Creative doesn't want to get emails intended just for Customer Service and vice-versa.  So it would have to be additional Teams/Sharepoints for the client.

Nobody thinks we can just procedurally keep people from storing files in the Teams/Sharepoints that were really just intended to be a distribution group, regardless of special naming conventions or whatnot.

How do other people handle the distribution list vs file storage issue?