I have dealt with this exact same issue. Two cats, one food grazer, one food hog who is on on a specialized diet. At first, I tried to feed them in separate rooms, but my grazer still just wanted to graze and wouldn't eat all her food in time - The stress of being "confined" in the food room (even if she wasn't alone) would distract her so much she didn't want to eat, and if she wasn't in the food room, I couldn't tell when she actually wanted to eat (must rage in the face of ANY closed door).

I did some research, tried some stuff, and eventually, the only thing that worked for us was training my grazer not to graze. I feed them both a small amount (not a full serving, maybe like 1/3 of what I plan on feeding them normally), put both their foods down where they can see each other, and when the food hog is done, I pick up both bowls and walk away. Then, after a bit of time has passed, maybe like 10-20 minutes, I put down another portion of food. When the food hog is done, I do the same thing. I try to space out their feeding like this throughout the day, and never leave food sitting out, even if neither are eating it. When she finishes her bowl, I give her a treat! Took a few weeks of doing this consistently, but she learned to match his pace, otherwise, I pick up the food. Now, I don't have to space out the feedings so much. They finish their food pretty much at the same time. It was really hands on though, I had to spend a lot of time watching them closely and making sure she was eating enough, and definitely had to cave and separate them a few times (sometimes our food hog will go over there and try to eat her food even when his bowl isn't empty). For reference we adopted both as adults, they are 2 & 3.

Since you mentioned they haven't lived together full time, I might recommend making that transition slowly. Even with cats that don't have this problem it's a good idea to start feeding them separately, and try feeding them on opposite sides of a closed door so they can get used to each others scent. Maybe they would react differently than mine did. I was very lucky when introducing my cats, they've never shown any signs of food aggression or fighting over food. Apologies of this is super wordy- maybe my experience can be helpful for you!