A 4 bar airport have any chances to flight to be full booked ?
Yes. Of course not an a380 but an EMB or an A32x.
Depending on which country you are in, you can grow a 4 bar airport into a mega hub.
RNG MYANMAR and started with CRJ 1000 NEXT GEN
Started with CRJ 1000 next gen er (5) in Myanmar RNG
And don’t forget someone in the same server making Pyongyang (3 bar) a busy hub
But if transfer is impossible in one airport, then it cannot be used as “hub” even if it had 10 bar.