Winds of Chaos

RAW describe in-fighting and weapon length modifiers as optional rules, p. 297.

Does the in-fighter talent have any usage at all without these optional rules?

Not as I read it, I believe you are correct. Although your GM may decide to give a circumstantial bonus to wrestling or knife fighting or hand to hand disarm tests if one opponent has In-Fighting and the other does not.

he is entirely correct, the talent only addresses the optional rules mentioned regarding range, and none of the modifiers enter play elsewhere in the book (in fact they're not even mentioned regarding unarmed combat, meaning you can bareknuckle your way through a pikeline without those rules!)