As others above me have mentioned, the Matchmaking mode for an easier difficulty of the Raid provides a good stepping stone for finding team, learning the mechanics, and going through the content.
It works on several levels as a sort of litmus test; if a team made through Matchmaking cannot complete the Discovery Raid whether it's due to communication, gear, or skill, that same team likely would have had those same troubles if not more on a higher difficulty. Sure, that team might have difficulty on the hard Raid, but by then they have worked together before, completed the Raid before, and may be more familiar with the builds everyone is running - and all with random players.