I do not think the numerics have a role to play here. Otherwise this would be the case in all the countries with Joint Chiefs. The US Army certainly outnumbers USAF, USN, USMC etc. The same goes for the UK etc. etc.PA is 550,000+ where as PAF and PN are in thousands. No wonder COAS takes the lead.
My own belief is that the primary issue in Pakistan is the Army's unwillingness to cede operational command of its units to officers of other sister services when they take up the CJCSC post. This is partly because of the history but perhaps it is also the reason why the post of CJCSC has become more relevant with the advent of the nuclear age in the sub-continent. These assets are going to be more evenly distributed and the strategy and employment of this strategic capability has been thought about from a "joint" lens compared to the conventional capabilities.
Gen Bajwa should have never been given extension. For that matter, the same with any others. There are plenty of other officers who can take on the mantle and continue. When we don't do these transitions right, it actually comes across as a weakness of the institution and not the strength of the individual as it is sold to the nation.i think gen zubair also deserves extension if gen bajwa is given extension
For each CoAS, there are at least a dozen qualified souls in the Army to take on the job. Our CoAS should also move on (credit to Gen Raheel Sharif) realizing that they are not indispensable.