Sounds like they just want to do that site, regardless of what your certification, comfort level, and experience entails.
Because it is your first ocean dive, it's smart to have a DM around to deal with any unexpected differences between ocean and fresh water, so good for making that decision. But a DM shouldn't try to push you beyond your comfort and experience level for your first ocean dive. Let them know your apprehensiveness and the reasons. If they don't offer alternatives, that would sound a little sketchy (and you're paying them extra).
The thing about DMs is that they vary so much in their competency, and there are so many. I've seen amazing DMs, and I've seen DMs that are just too reckless. I've had a DM try to convince me to go into the water with equipment that wasn't working properly. You've just got to be wary.
A lot of people do their AOW right after their OW in PADI. I'd probably recommend more ocean dives before doing another course, though, just for the experience and to increase your comfort with the ocean.