We have been over the public proof part. Remember US has interests in Balochistan - mainly restricting China from using Balochistan. The reason for that is US faces losing hegemony position in the world with the rise of China. China can use Balochistan to a great advantage. And yes that means US may be involved in Balochistan insurgency. So US is pressuring Pakistan to not go public with the evidence. We have insiders within ISI and army who say they frequently give proof to government about indian involvement - not just about Balochistan but also about TTP.
Also, when they say they have proof, they do show it - to the respective states which are india, US, Afghanistan, so on. And again, using credibility as a benchmark is naive because other states will only acknowledge what they want to acknowledge and won't acknowledge things that are not in their interests to acknowledge. We have been over this and I am sure you have heard about this before.
As far Hafiz Saeed goes, the allegation against him had to do with JuD and in particular that he was involved in planning of the attack (if I remember correctly). There was no proof to suggest that.