SharePoint Not Working for Graphic Design Department

I also work in a similar environment (but as the Sharepoint guy) and can share a few ideas.  

First off, SP can be made to behave like a file server set up but making syncing the "way to go" is the wrong path to take. Msft's sync functionality is flaky and duplicating tons of files locally is inefficient, wasteful and defeats the purpose of paying for cloud storage. 

My advice is explore network locations which allow you to open/save files directly from SP via windows explorer only when you need them and provides by far the most familiar and friendly user experience. For example, I work in Adobe products like Photoshop and NEVER have to save anything locally. I simply "save as" and then select my SPO shortcuts in windows explorer. Very easy, very efficient and so obviously the way cloud storage should work.

If you need to collaborate on content across multiple devices (as we do), then consider syncing one project library in a regular SP site - not OneDrive. OneDrive is also just a library but it comes with a "special" set of permissions which makes sharing more difficult so avoid syncing OD at all costs. As an example, when my design/web team tried using OD to collaborate, Msft's odd definitions of "shared with me" and "shared with everyone" just confused everybody. Once I suggested they use a regular SP site library, it worked exactly as they wanted. Unfortunately, Msft decide to cash in on the OneDrive brand and using that name for their sync client is highly misleading and once again, confusing. 

So to recap:

Create network locations when working on one machine.

Sync a project library only when collaborating on assets and either clean it out or delete it when done.

As you probably realize, your IT guys have drunk the koolaid fed them by Msft. Msft clearly doesn't use SP in the real world the way we do and their recommendations to me often seem totally pie in the sky and definitely not born of experience. So  never take Msft's word for anything - be willing to experiment and try out different ways to get SP to work the way that suits you best.