Let's put the 5th-gen stuff aside and look at the FC-31 for it actually offers: 8,000 kg payload, twin engine, 2,000 kg concealable, apparent ability for low-level penetration flight, AESA radar and integrated EOTS. If that alone is available and fully usable from 2023, then I'd be surprised if the PAF would skip that in favour of the Mirage ROSE and Mirage 5PA in the strike and maritime operations role, respectively.
Just imagine the idea of equipping 2 Ra'ad II ALCM or 2 AShM in the internal bay and then super-cruising at low-altitude to launch points over land or sea, then firing, and then being gone by the time the adversary tries intercepting your munitions.
Even if one wants to develop a separate FGF, fine, but it'd be wildly curious to keep flying the Mirage ROSE and -5PA when you could have the FC-31, even as a bridge or interim fighter until the PAC FGF comes online.