The Rafale is an impressive plane, and one that should not be discounted, in particular its EW capabilities.
Pakistans deterrence does not rest in having a plane that is "better" than the Rafale, it is in her ability to strike into India and defeat the narrative of India being a super power and the region being its "back yard" etc. It is the ability to hit Indian pride, that is the core of deterrence. What stops and scares India is the counter strike. PAF strikes in Feb 2019 stopped India in her tracks, as it was very difficult for India to explain to her population that a country 1/8th their size managed to come into airspace protected by the IAF and bust up the place, and return with no consequences. It will be a long time, before any Indian PM will be confident enough to risk that. The proliferation of cruise missiles makes it more difficult for India to hold the narrative of her own perception of herself. Imagine, long range cruise missiles hitting New Delhi in a counter strike. India simply didnot expect PAF to strike back in Feb 2019, and expected to hold the narrative, escalation ladder and initiative. They lost that..
No matter how good the Rafale is, going into contested airspace against SAMs, ground based radars and AEWCs is going to be a tall ask. The aircraft is not invulnerable and can be countered. There may even be losses for the PAF in contesting airspace occupied by the Rafale, but it wont be a 1 way street. The PL15 and to some extent the AMRAAMs will see to that. That is the deterrence.
Block III with an AESA radar, and PL15 will pose a serious threat to the IAF. It may not win on the "specifications war" against the Raflae but that is not how combat operates anyway. The Block III will be good enough to take on everything India has in her arsenal as of now, and beat it. Rafale is a challenge, and we may need Block IV as a response.
The Su30MKI is a brilliant plane, and very capable. But, poor deployment and tactics by the IAF caused it to be shot down in Feb 2019.
IAF tactics, and operational deployment skills and abilities will NOT change with the arrival of the Rafale. It is questionable if they will be able to get the best out of the platform they are procuring. They have always struggled in this regard.