لَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِٱللَّٰهِ
The Sahaba (RA) questioned the second Caliph, Omar ibn al-Khattab (RA), on why he had an extra cloak, or why he (RA) rescinded the stipend given to mothers, or why he (RA) folded newly conquered land instead of allocating it to the soldiers, and so on. And Umar (RA) responded to every single one, either by showing his justifications from evidence, or (when he was incorrect) by changing his policies.
Accountability runs in the veins of Muslims, so don't be surprised that when Muslims (given the agency that the Pakistani elites deny them) demand answers to questions about their public affairs.
The issue at hand isn't about who has the authority, but about applying the concept of ٱلْأَمْرُ بِٱلْمَعْرُوفِ وَٱلنَّهْيُ عَنِ ٱلْمُنْكَرِ (i.e. enjoining the good and forbidding the evil). Believe it or not, this idea isn't limited to the height of your pants or length of your beard, but on matters of public affairs, such as where the nation's money is being spent, whether it's being spent well, and what the returns on that expenditure.
This is how strong and prosperous societies function, and the elites of said societies know to respect it. The ones "venting" here want to see a Pakistan that not only rivals India, but mops the floor with India in every single domain, from science to sports to everything. For that, we need to establish standards, and the most crucial one is accountability of one's leaders, be it military, political, bureaucratic, or judicial.
We are expecting the evidence because the service chiefs themselves made the claim. Do you have no understanding of the basic concepts of "proof" or "evidence?" When one makes a claim, they should provide the evidence to substantiate it; otherwise, it is a baseless claim.
We "venting" lot would prefer our service chiefs to provide evidence so that they do not make themselves and Pakistan a laughing stock in front of the world.