All around a good post, but I disagree with lowering the amount of players needed.
It's super easy to get 5 members. To get 5 good members on the other hand is pretty hard, and that's not the game's fault - you need to build strong connections with people to make that happen. Most often you will have to live with having a lowbie or maybe even 2 for a while before you can start building your troupe.
It's not something that takes 30 minutes to get right. Having a solid foundation in a gang is something that takes a lot of effort and time.
Other than that, I think you have to realize that the game is built in such a way that low tier gangs can have super high level players. Meaning that even if you restrict certain things to accommodate the mid to low tier gangs, there will always be a select few that reign supreme. The only thing that actually helps here is hard work - you can't just expect to be one of the best in something just because you restrict the absolute top from joining.
So yeah, conceptually I think you're right, there should be something to for low-mid level gangs to duke it out on and I think it should be easier finding wars in tournaments. But I don't think your particular suggestions will make much difference.