You can keep saying they did not do it but it does not change the fact that they did and do.
They first started sending assassination squads to kill the old regime members who had fled Iran. Even DHA Karachi was not spared where there was a mini-war with rocket launchers ( I have seen those houses with my own eyes ). This was in the early 80s when Karachi was relatively peaceful. Not sure what you mean by not buying.
After it became a challenge to send their own kill teams they turned to the local Shia population and began developing and funding groups within Pakistan. Relatively quickly the Saudi Machine kicked in, which btw was already well established but focused primarily externally towards Afghanistan and elsewhere. They took that pre-built infrastructure and turned inwards.
Jhang became a major flashpoint but there we allowed another external third party to get involved and it was not India.
Lastly I agree I am hoping Iran will see the light with a little nudge from China. But in this entire calculus what everyone here fails to see is the Persian effect. Notwithstanding the revolutionary issue with the Iranian regime, the key here is that the Persians have a bit of God complex. They have a rich history that they always bank on. Even the Mullah's will revert to their fire and light worshipping ancestors when they need to establish their unique culture outside of Arab influence and that cultural difference has more to do with the Shia and Sunni split than anything else. The Persians wanted a dogma that was not subservient to the Arabs, so they took a political difference and gave it a religious color. The rest is history.
It is this Persian mindset that thinks it can tangle with everyone, so though China can have a moderating influence, dont discount Irans long arc view of the importance of a weak Pakistani State to advantage Iran. For them a strong Sunni state is worse than a strong Hindu state because a Sunni state has the greater potential to materially impact their system of governance and politics than a Hindu state.