He didn't appear, but his presence was felt. The central theme from the beginning was good vs. evil/nature vs. nurture. Colossus always represented her nature side with Belasco being nurture. It's important to have somebody that fundamentally good-hearted to make it work. I'd have to go through a bunch of issues to find examples, but it came up pretty much any time either Bobby or Raine was scared of her after seeing Limbo. Certainly, I'm talking about the Claremont run, not the Simonson run.
It's not necessary for the movie, I agree. I thought, given what they had done, they might as well not have made Havok and Cyclops related. I also think if Siryn were to appear (likely connected to Deadpool), she won't be connected to Banshee. But I like these family connections and I'd prefer a more modern New Mutants movie to help separate it from the young X-Men cast.