How exclusive are frats

Top tiers - pretty exclusive, if you didn't dirty rush or don't know anyone in these, it's next to impossible to make it far while rushing them
Upper mids - fairly exclusive, dirty rush and knowing people really help, but you still have a chance (low) if you don't
Mids - somewhat exclusive, dirty rush and connections help but you can still get a bid without them. They get a lot of good guys who were dropped by tops/upper mids
Lower mids - not that exclusive, get a lot of guys who were dropped by mids
Bottom tiers - not exclusive