The movies did as good a job as could be done considering they started coming out before the books were finished. And let's be honest, it could have been far worse (looking at you, GoT). Despite the movies having to cut out a lot, it was still really done well. Unfortunately, Ginny's casting was done well before the movies knew the greater role she would take on in the books. To that point, she's hardly seen into the movies until it becomes known that she's going to be Harry's lover interest. So we agree there. It was hard to manufacture the connection when the movie director's always treated Ginny like a background character. And unfortunately, the actor wasn't strong enough to pull off the lost time in the later movies. This is one of the things I'm looking forward to the TV series correcting. Ginny will surely play a more prominent part in the TV show at least starting with book two. From the movies, you almost forget that she's a big part of that storyline. She's there in the books. The movie makers just didn't know she'd be so important and it shows.
Respectfully, you've misinterpreted the scene you referenced. It wasn't them attempting to be more than friends or hinting at them wanting to be more than friends. Quite the opposite, that scene is specifically about Ron. It was an attempt to cheer up his friend who's obviously missing the guy she's in love with. The scene ends on a somber note. The unspoken message that both understood was it's not the same without him here. She knows what he trying to do and appreciates it. He understands that she's trying to make the best of it and not show how it's getting to her and appreciates her for sticking through it. It's a love and mutual respect for their friendship being highlighted in that scene, nothing more.