Why does Pakistan need a stealth fighter to counter stealthy American helos?
You can say that the American raid demonstrated how stealth assets could be used effectively to penetrate deep into what was believed to be well monitored airspace, in which case a stealth fighter would be very useful for the PAF if it wants to penetrate enemy airspace undetected.
But to suggest that the J20 would somehow make Pakistani airspace immune from incursions by foreign stealth assets does not make much sense. To counter stealth assets, you need to be able to detect them before you can try and vector in your own assets to intercept them, and it is only then that a J20 might be useful.
But if you cannot detect hostile stealth assets, having J20s around will not do you much good.
And considering how China has not even released the J10 to Pakistan and/or Pakistan cannot afford J10s, it is highly questionable whether a) the PLA will allow the J20 to be exported to Pakistan, and b) if the PAF can muster the funds to pay for them even if the PLA oks the sale.
But since the J20 is at least another 5 years off from even joining the PLAAF, any talks of PAF purchases of the type is pre-mature at this stage at the very least.
Personally, I think the only way PAF would get access to a stealth fighter is if they can team up with CAC again (or maybe even SAC this time) to develop a new medium weight 5th gen, similar to have the JF17 was born.
Given the PAF's well established and good relations with CAC, such a switch is very unlikely, but if SAC offers a 'stealthy' design that the PAF can buy into immediately and CAC is too busy with the J20, J10B, JF17 and all its UCAV projects to be able to offer a similar joint stealth fighter for PAF, SAC may be the only option unless the PAF is willing to wait many years.
But in the very best case scenario, the PAF is at least a decade away from seeing any stealth fighters in its ranks.