What is it you take issue with, specifically?
That your idea of what the game is like is 100% based on watching streamers.
His point was that the entire economy of SC trade is more or less determined by whatever the top 1000 or so people in SC trade are doing. You can opt to play SC trade like SSF if you wish, except occasionally trading for some unique item which would otherwise be irritating to obtain, but this doesn't change the fact that the underlying problem is that the entire game is balanced around SC trade. This means that regardless of which game mode you choose to play on (SSF, HC, etc), what goes on in SC trade will impact how your game plays in some way or another. I have played the game in many different ways, mostly to keep things interesting, by experiencing the different flavors of PoE. This league I tried out group play, so I do actually have some perspective on what that is like. From an economic perspective it gives you such an overwhelming advantage relative to anyone else doing it that it is like a completely different world. This is a screenshot of what my gameplay looked like, for perspective.
You cannot see anything, there is just loot all over the place and yet despite what people will tell you, there is actually a lot more to manage in group play than there is when playing solo. You need to constantly keep in range of everyone else, because if 1 person is out of range they will automatically die and then the map is bricked. Each map takes significant investment (we were investing 4+ ex into every map we ran) so you don't really want to brick them, but you make 20ex+ back per map you run. You cannot move too quickly, because otherwise you will encounter server issues which will either cause significant rubberbanding, or someone will crash. When entering zones like Alva missions, you need to time movement to take advantage of the grace period so that you do not die, because after moving on the first server tick your auras are not active on you and so if something hits you you will instantly be deleted. All this + having to coordinate with 5 other people and having the additional management factor ends up making for a lot more work than just playing ssf but obviously, it does enable you to do whatever you want after that point. After a couple of days like this only playing 1-2 hours in the evening I was sitting on this:
And as I said, I was very casual about this and was only playing 1-2 hours in the evening, compared to people running for 5+ hours and treating the game like a job. Its very easy to see how playing like this gives you such an overwhelming economic advantage in a trade league that you can basically determine what goes on in the market. I am not sure if I would ever do this again though, its quite draining to do and feels a lot like work. It gives you complete freedom to make whatever you like in PoE, but I think that part of the fun in the game is playing with restrictions and not being able to almost item edit your way into whatever you like.
The problem with it is obvious though, players who play like this funnel the entire economy into their characters and saturate the market to a level that would not be possible if this type of gameplay did not exist. Since the game is balanced around SC trade and since the entire balance of SC trade is determined by these few players, the experience of everyone who plays the game is dictated by how they play.