How so? While I don’t think that bitless should be allowed in dressage because it is not the same outcome and you should not have contact, the same movements can indeed be performed by a horse who has never had a bit.
This is reining, but this horse has never even worn a bridle and performs collected movements while “round.” Note the head carriage during these movements despite never wearing a bridle, although it is obviously not “on the bit” and missing that component of what makes competitive dressage.
https://www.youtube.com/watch?v=ALQlS0MntNg&ab_channel=LukeGingerich