I don’t think grouping should be disabled entirely but I think it should definitely be only full groups can join or you can join solo with other solo players.
It does take the fun out of it, like Tovi and you pointed out, when you solo queue and you get in a group of 3-4 people all in the same guild. Very rarely do they vote for you.
Make it like the Megadungeon is right now, you can’t queue for it to fill in with random people, you have to form the group to enter manually. If that makes sense.