I'm pretty sure that if Tomoya had told Sunohara his sister was coming, he still would've searched a girlfriend, and his route would keep going like in the game. But instead he didn't know shit so in the end he didn't have time to get in touch with delicious Sanae.
Besides, it doesn't matter if it's useless, I still wanted to see that fight with Tomoya.
Why did Kyoani do this art anyway? Teasing faggots.