Logan's injury wasn't about furthering Logan as a character: it was about Rory. It enabled her to stand up to Mitchum and assert herself. We'd all been waiting for her to finally lash out at Mitchum and this was the lever she used to do so.

It gives weight to her relationship with Logan, establishehes her backbone and heightens the drama when she turns down his marriage proposal.

That plotline was integral in Rory's growth as a character.