The best defense is a strong offense.
The J20 would work extremely well for the PAF, especially in the deep penetration force multipler hunter role you just described. The J20 was tailor made to penetrate deep into what the enemy considers 'safe' airspace, where the enemy has overwhelming numerical superiority and extensive surface based defences, and kill their most valued assets and then super cruise home before the enemy could bring enough forces to bare to overwhelm the J20s.
It's stealth should allow it to circumvent the bulk of the enemy's defences, but it will also have the raw performance to dominate any enemy fighter it might have to punch through in order to get at its preferred targets and then home again.
A small force of J20s would allow the PAF to take the fight to the IAF over Indian territory and tie down large numbers of IAF fighters protecting their tanks, AWACS and transports so they are not taking part in offensive attacks over Pakistani territory.
Being able to successfully kill IAF tankers and AWACS would also give the rest of the PAF a huge tactical advantage over Pakistani territory by reducing the range IAF fighters can operate and also potentially giving PAF local information and coordination superiority.
Sounds like a dream scenario for the PAF and the IAF's worst nightmare bar maybe having to fight China and Pakistan at the same time.
If China offered Pakistan the J20, Pakistan would have to be mad to not snap it up before the Chinese came to their senses.
One of the issues Pakistan would need to address if they want 5th gens (most probably J31s since the J20 won't be on the cards until China has 6th gens in advanced prototype stage, just like how the J10 wasn't on the cards until the J20 was close to first flight) would be the security of the airbase for those 5th gens.
Having 5th gens is not much good if the enemy can take them all out on the ground in an alpha strike. So Pakistan would either need to invest in long range SAMs (I have still not heard a good reason why Pakistan has not done so already other than maybe because of a lack of funds) or think about basing its 5th gens outside of its territory in peace time.
If Pakistan and China can reach an agreement for the Chinese to lease the PAF an airbase in China close to the Sino-Pakistani boarder, and for all 5th gens China sells Pakistan to be based there, it would make a 5th gen sale far more likely since China won't have as much security concerns as it would if the planes were based in Pakistan about CIA operatives crawling all over them. Pakistan would benefit from getting 5th gens and also from the peace of mind in knowing that the Indians would have to be mad to attack said airbase as that would be guaranteed to drag China into any conflict. Such a deal could be done in parallel with Pakistan leasing a naval base for China to home port a fleet in the Indian Ocean.
I think such a move, or something similar, is very much in the back of the minds of the Indians, which is one of the main reasons they have resisted American temptation to join in with its containment strategy against China because they did not want to make a formal military alliance between China and Pakistan a no-brainer for Beijing.
Similarly, Beijing does not want to make India feel so threatened as to go running into Uncle Sam's eager arms.
Right now, there is an uneasy balance of sorts. Both India and China knows that they, and each other, can do things to make each other's security situation a great deal more precarious. So neither side wants to push the other so much as to break the current equilibrium and cause a massive escalation in tensions and worsening strategic security position to the detriment of both sides.
But I digress.
