There are different yardsticks that we should measure each of them by.
Saim Ayub - He is fast going the Mohammad Hafeez, Afridi route. He realizes he is an accurate bowler and with his bowling improving he can have a spot occupied in the playing XI. The problem is that once a player goes down this route where the primarily skill is substituted for Jack of 2 different skills then that player in my opinion cannot be categorized as a match winner. Jack of something cannot be categorized as a match winner. The problem is that in Pakistan cricket we have glorified the Jacks in cricket with likes of Afridi, Hafeez, Malik achieving legendary status in the country. Yes the likes of Afridi has singlehandedly won Pakistan some games but on pure probability basis if you are to play 500 games then its likely you'd play a winning hand in 20 or so games. Bottomline is Jack is not a dependable cricketer in the long-run. Therefore, Saim needs to sit down and realize if he does away with his batting prowess there is likely to be a substitute waiting to replace him. If I'm in PCB I would simply walk to Saim and remind him of his centuries in Australia and SAF and how those innings more respect to Pakistan cricket and fame to him, never his bowling would be able to achieve that feat. Hopefully he regains his batting form as that is the Saim Pakistan cricket needs.
Usman Khan - A very poor cricketer that has been continuously playing at top level for already too long. I can admire his dedication to Pakistan cricket but dedication alone won't make him an international level cricketer which he unfortunately is not.
Salman Agha - Gold player in ODI and test cricket. Isn't needed for T20Is. PCB has got captains in wrong order for ODI and T20s better for Pakistan cricket to rectify the mistake and hand Agha ODI captaincy where he'll thrive and give Shaheen or someone else T20 reigns.
Fakhar - A mercurial cricketer renaissance of 90s era. Him along with Maxwell I believe are only players of this mercurial power. Fakhar in a team like Australia would thrive and be a bigger name as that is a solid team where team is not necessarily depending on him for results much like Maxwell but when team is in a hole they can singlehandely dig them out. However in a country like Pakistan where you are actively relied upon for results then inconsistencies can be frustrating. Either way we don't have someone superior to Fakhar waiting in wings so better to stick with him and give him confidence to ensure he is in right frame of mind when taking on field.