I definitely agree with your first sentence, $5 mil/yr is too much. As far as accountability, T-Mac keeps playing him. This tells me he either doesn't see an issue or doesn't trust that anyone else on the roster would do better. That's not really an Iafallo issue.
As for the examples, I was more just showing that even top heavy teams use traditional 3rd line and middle 6 guys in their top 6. But your point about Iafallo being stapled to Kopitar, unlike the examples I provided, is fair. I've seen people refer to Iafallo as Kopitar's Pascal Dupuis. Seems fairly accurate but Kopitar likes playing with and they work together. If you can resign him to a decent rate, just keep him with Kopitar as they slide down from top line to 3rd line over the next 4 years. It wont cause cap problems.