I have no real knowledge of Shaheen's product, their service nor their punctuality - however I'd say in one regard they hold an advantage over Swefly and UKIA in that they are a Pakistani airline.
Can't imagine too many punters of non-Pakistani extraction wanting to fly to Lahore, Islamabad etc, therefore a Pakistani airline used to the customs and culture of Pakistani life is surely beter placed to serve this market.
bmi have surely got more lucrative/easier places to fly to.