It's not just streamers and other top players that are the issue, it's a fundamental design issue. I just don't think you can have (a) a public event in a public space that encourages emergent gameplay, i.e. a team of 3 starts it and the rest of the zone joins in and completes the activity and (b) a challenging endgame activity tuned around high level players.

In (a) you have to account for the large skill and level gap in Destiny, which means tuning around the average random player that may be in the zone, which is likely going to be someone at the soft cap and of average skill. According to statistics, only around 20% of players have completed The Leviathan, so these players are not necessarily going to be able to contribute in a difficult activity. It also means players who do manipulate matchmaking are going to have a super easy time, invalidating difficulty and making it so it can't be a rewarding activity.

In (b) you essentially have another raid and need fewer variables in order to tune the difficulty. So what we have is difficulty tuned around well equipped Guardians in order to keep the difficulty up throughout the life of the content. That will keep lower level Guardians from being of any value, and since it's a public event that player takes up a spot that could otherwise be used for a better equipped Guardian. This has lead to toxicity, as lower level players are being asked to leave zones (and potentially their opportunity to participate in EP) so players can manipulate instancing to build large pre-made groups. It has also lead to lower level players avoiding these patrol areas because of repeated failure to clear wave 1. Unfortunately, these issues go against the entire point of a public activity in a public space.