Most of the content you are going to need to play with other people if your goal is to rank up (which is the point of destiny). The good thing is, 90% of it is totally fine playing with random matchmaking. I've sunk hundreds and hundreds of hours into Destiny 2 and played nearly all of the online content with random matchmaking. The thing that stinks about Destiny 2 though is that the funnest content to play (dungeons, raids, and high level nightfalls) don't have matchmaking. Which is honestly what pushed me away from the game. I got tired of having to go on the destiny app or a 3rd party app looking for someone to play content with. If they had some system of matchmaking for higher level content, I'd probably go back.