I disagree. Here's the thing: if the only reason people are reading your comic is to find out if they're gonna end up together, then there's something wrong with your story. You were right when you said:
Think of any action movie or battle anime. The good guys always beat the bad guys. That's not the point of the story. The story is about how you get there.
So no, I don't think drawing couple art is a problem. It shouldn't take away from the story because that's not the story. The story is how they get there.
THAT SAID, it's a bit overdone. I think it would be far more interesting, if you're going to draw one-off stuff, to draw "situations" from their current story status. Let's say you've got Alice and Bob. They haven't dated yet. You could draw Bob looking at her from afar. You could draw Alice getting jealous of Bob's new girl friend. Now they're dating. You could draw them having coffee. Riding a rollercoaster. Now they've moved in together. You could draw them doing the dishes...
You get the picture.
But I guess if you just wanna draw NSFW stuff... it is what it is.