We are timeless, bound as one, we cannot be silenced, as our song lingers on.
The 7 on 7th playlist is not ranked, the way to tell is if it has a number next to the playlist rank symbol next to your name while searching.
The only playlist you can get Ranked FFA achievements on any-more is Lone Wolves as Bungie no longer does Double-EXP weekends so Mythic Brawl is not an option.
I think DLC FFA was also ranked at the time, I wish we could return to the days when you could go on a ranked objective playlist or have 6 people on your team in a ranked playlist.