I feel like I am the only one listing my group as “completion”
I would gladly join your group if it says completion, but I have yet to see a group listed as such except mine.
Are completion groups that rare?
I only join completion groups because the go go timing mentality gives me anxiety (I alrdy have enough irl)
So pls if ur like me and don’t care about timer, pls list your group as completion and I will join them. 
Usually I like to start my group off with something like this:
“Hello and Welcome. I understand we are all in this with the goal of timing it but I will be happy with completing it overall. Thanks”
and usually anyone who isn’t chill about it will leave
i’ve seen more and more groups list it in their description (including titles with “No Leavers” and such…i think it’s great to see that tbh because it attracts like-minded players to the group.
to answer your question - i don’t think they’re rare anymore… in my experience, players don’t seem care about failed runs as much this season…compared to SL days anyways 
I don’t run completion keys super often unless it’s on an alt that’s low on the totem pole, but I do like to run them on Mondays.
I never like hearing that. It sets the expectation of failure and puts your group in the mindset that you don’t need to time it right off the bat.
I typically don’t run groups with a lot of pressure when I’m just playing to relax. If I want to push, I will invite people that don’t need to be welcomed.
My push group is that biker that eats the spare bolts off of his harley and able to withstand massive amounts of pain, a karen who absolutely cannot HANDLE IT when we stand within 5 yards of her and will scream about it, a young teenage boy who can’t admit that his anger problem is rooted in depression caused by lack of sunlight and exercise - fueled by the competition of gaming, and a man fully addicted to slamming 5 hour energy drinks to get through his work day at the office because he had to slog through the lfg for 3 hrs and finally completed his single weekly dungeon at 2am (he plays a non meta obviously).
Tbh I respect your mindset but I will not join a group if we cant time it do I despise the m+ timer for rushing me? Yes. Why do i deal with it? I dont know.
Hearing that is a good thing though. It lets you know that the group isn’t for you, and it attracts other players who are more interested in finishing than timing. I’m 100% in favor of communication like this that helps people build groups with players that have the same goals. It prevents a lot of friction.
Sometimes I join completion 20s.
A lot of groups put this in the note, instead of the title.
My experience is most groups will try to finish it if it isn’t overtly doomed early on by wiping to something that isn’t a common group killer. For example, wiping on the first boss in Azure Vault is usually an incredibly bad sign of success for later bosses that are much more demanding overall.
Also, BR players just love to immediately leave at the drop of a hat, even if you don’t wipe. I’ve had them just randomly be the first death on avoidable trash mechanics and then bail.
Your lack of horns is incredibly unsettling. I do not want to join your completion 20 out of fear of the smooth scales on your scalp, not because of my gear or skill.
Yeaaaaah suuurrree 
I also hopped on a space rocket and went to the moon.
Completion is setting the expectation of wiping, so I avoid those listings.