The only outdated thing in Halo is that there was no quit penalties in unranked playlists, and if there were, it was shit (Reach's 15 minute crap). The community was never punished for quitting unless you were in ranked, and well, right now there is barely any ranks.
MCC is doing it right by instituting a system wide quit penalty and I hope it continues into Halo 5 and quitting gives even more penalties. JiP would just be a band aid and encourage players to continue to quit.
"Oh I don't have the Sniper. Quit"
Join in progress next match
"Oh I'm down 5 kills. Quit"
Join in progress next match
"Oh I'm down 2 team mates. Quit."
JiP does nothing to help fix matchmaking.