You might have 1 or 2 things not quite right here. You can do story missions in private, with as many in your team as you want up to 4. You have to play free play and do strongholds with 3 others. If you're a 3, there will be 1 random. It's not a big deal.
You'll only get loading screens when you enter into the deeper locations off the main map in free play, but randoms cannot pull you through to them, not even if you're doing a World Event that goes down one, as you can back out of one of those whenever you like. You'll get loading screens when you try to enter areas that are off limits for the demo, but you can avoid that by checking the greyed out area of the map and by simply turning around before the countdown ends.
"where there person has clearly run it 20 times already and keeps running off ahead" - that's not free play, that's some sort of story you chose from the menu or the stronghold. Strongholds are repeatable content, people are going to get good and know what to do really quickly. the game is based around rinsing these. You can't play these private.
The menu is a bit crap, and it does that annoying nag when you want to start a story in private, and that's easy to cancel out of and end up making public without even reading it. BTW, entering these events and wandering off because something caught your eye in a public game is damn annoying for the people stood waiting at a gate that won't open until you & your pal finally get their backsides to the trigger point ;-) so it works both ways.
I'm not sure, there have been far too many times that I or the other 2 people I played with are being forably teleported with a warning by being not very far from the furthest person. There's even official gameplay of someone getting teleport warnings by mearly being a stones throw away from the lead character at a check point.
Also, I'm not sure being a pedant about if it's a mission or stronghold or whatever has any weight about me hating having to play with a random in my group of friends. The argument I'm making is the entire thing is shit to begin with when the game already supports scaling and private mode. Why close that off for certain activities? It seems to abitrary a decision and impacts nobody if they allowed it.
Lastly, works both ways? I'm not sure it should be like that, the 3 of us wanted to do an activity in private like we had just previously done in a mission, the game won't let us. Fine. We want to play at our own pace for the first run and not at the uncontrolled behest of someone random.
I've never seen this forced "follow the leader" in a game before.
Edit: I had this problem last week as well playing solo in free roam.
https://www.resetera.com/threads/an...-fly-freelancera.95459/page-110#post-17300714
All I did was see a camp of enemies, wanted to nope out but it would'nt let me.
It wanted me to finish, I wanted to try find that other person out in the world.
Can't defend that. Imagine playing destiny 2, seeing as public event pop up but it's just you; you try to leave but it won't let you.
It keeps teleporting you back over and over until you've finished it, but it wont expire, it resets every time you die or leave.
Luckily they understand player freedom and let you ride on by to something people are actually doing.