Hi Lewis. The projects you're talking about aren't worth getting into an awkward debate over. I'd just hand over the stems and tell him, like you already did, the OMF isn't a realistic option.
As an editor, which is all I do now days, sometimes I get stems, sometimes I don't. Depends on the company and the client. Sometimes you get an inexperienced assistant who requests the stems. Sometime's I get CCd on the email asking for them and the conversation can sometimes go like this...
Assistant: "Hi Audio Designer. I'm an Assistant at such and such and we need all of the audio files you used for the project. Thanks."
Audio Design: What the hell? Consolidated? Dumped in a folder?... "Hi Assistant. How would you like all those files delivered?"
Assistant: Uhhh. "Hi Editor. I was told to collect all the audio files used in the project. Any suggestions?"
Editor: All the audio files? What the hell?... "Hi Assistant. What are the files being used for?"
Assistant: "Hi Editor. We need them for mastering and archiving."
Editor: "Hi Assistant. You can ask for stems. That should cover all your bases."
Assistant: Cool - a new industry buzz word. "Hi Audio Designer. We'd like the audio files to be stemmed."
Audio Designer: Stemmed? "How would you like the tracks split?"
Assistant: "Hi Editor. How would we want those tracks split?"
Editor: How the hell should I know? "Hi Assistant. You'd probably be fine with dialog, music, and effects. Might want to check with the Project Manager."
Assistant: "Hi Audio Designer. Dialog music and effects please."
Audio Designer: Good lord, when is this project going to be over? "Hi Assistant. Sure thing. I'll have them out by end of day. Let me know if you need anything else."
The Editor and the Audio Designer both live to fight another day - with another company.