Threat levels imo should be based on K/D and the whole matchmaking thing. As someone said already, gold players (these who are perma gold and never drop silver) are a completely different league, like invincible gods. They should always play only against other players from their league. Bronze/silver or even normal gold usually can't even touch these guys, they solo multikill everything. There are many people who will never reach that level or be anywhere close because they have some disabilities, play casually, don't have the best settings/pc or just don't care to tryhard and be competitive like many golds. Just let us play with people similar to us, and make them play against people similar to them, simple as that.
Missions are usually 2-8 players so it's not really hard to match proper people, i always see them when i drive around and if we had some phasing or similar kind of thing that would search on all districts then the current playerbase is more than enough for it to work.