1. But how did the Brotherhood of Steel make it though Legion lands? How did that ex-Enclave get through it and the Enclave for that matter? We simply don't know how but they did. It's very possible they went around Legion lands.
2. If people knew they couldn't get though Legion lands with drugs, they would simply take the long way around. If it's worth it, they would. You can go North or South and then move East to completely go around it. If it's really worth it, people would risk going though it.
3. There is also the possability people with the knowlegde to make it went through Legion lands only to make the Jet after they safely made it though.
1. Power Armor + Energy Weapons vs A newly formed Legion, I wonder who would win. Caesar states they can take care of BOS but that it takes a lot of soldiers doing so, and the Remnants in Vegas cut through Legion like butter in the Sahara. So a newly formed Legion? I think that Lyons Brotherhood and Enclave had no problems crossing that.
2. Then what was worth it? That's something I didn't understand any of them with. Was it really worth it for Harold to travel east? Was it really worth it for the ex-enclave dude to travel east? Was it really worth it for the Brotherhood to send that boy east? Was it really worth it for the Enclave to go to Raven Rock if they already had a Crawler? Was it really worth it for the BOS to go east considering the only piece of really good tech they found was Optimus Prime.
It's not just Jet with this, it's a nitpick I have for everyone who went from west to east, why bother? My only speculation on it is that pre-war the government built a machine which would magnetically draw idiots there. A complete idiot would get a compulsion to go there for no other reason than instict. Maybe that's why we have a settlement built around a nuclear warhead?
3. Now there is a good idea, that could definitely work. But, how does a person with that knowledge know what is beyond Legion? Why not just go south to Mexico or north to Canada? Seems unnecessary to trek across the entire continent just to be in charge of the Jet-business there. Just going north or south enough would do and one could establish a drug-empire, without having to trek across a continent.