The F35 is underpowered. They are developing a new engine that will bring up the speed.
Supersonic flight IS actually used during fights:
1. To quickly close the distance. This was actually employed by one of our Viper drivers against encroaching Russian plane.
2. To increase the range and lethality of BVR. A BVR fired from higher speed and height will carry more potential and kinetic energy, resulting in longer range and more force at impact. This is used by Russian Flankers.
3. To quickly escape after launching a nuclear strike. On of the factors limiting the max yield of nuke you can carry is the speed at which you can escape.
4. If your customers require a Mach 2 speed, you will build it just like u had to build the B version to fulfill market demand.
5. Gripen, a plane of similar class, has a max speed of Mach 2. If it is so irrelevant, then why did they put this feature on it?
This is the theory. Should it apply to Thunder? I will leave that for discussion. Personally, I am keenly waiting for the specs of Block 3 to be released.
I really think this whole debate of Mach 2 or 1.8 is basically making a mountain out of a mole hole.
@CriticalThought
1. I agree with closing the distance, though I have no way to validate the example you gave. Regardless, as is the case with our planes, esp JF-17 (as its being the one critiqued here), they are single engine with limited internal fuel capacity. No plane goes Mach 2 with fuel tanks slung under the wings or fuselage. Therefore at full afterburner, you will be bingo very soon if trying to sustain such a speed. Hence it might be useful in terms of interception or a quick egress, but with the geography of Pakistan as is and the distances that need to be covered from any FOB, the little bit of extra speed is not a make or break deal.
2. This is an important point and it is one of the ways the F-22 achieves superiority over rivals. It is able to fly higher and faster for longer duration and coupled with it sensors, able to execute BVR engagements from much greater distances then conventional 4gen fighters. However, to really be able to utilize this capability, the fighter has to be able to supercruise (that is fly above Mach speeds without the use of afterburners and thus reduced fuel consumption. No other aircraft is capable of that feet for any meaningful duration or flight regime (for eg, in a dive) while carrying a weapons load (have to carry internally so no 4gen planes qualify). Hence, while this point is true, and an F-16 or JF-17 etc shooting off a BVR missile at 1.4 mach would be at an advantage vs one shooting off at lower speeds, I don't see PAF or any other regional air forces, including IAF, to really use this at the max of its potential.
We also have to keep in mind that during any conflict, both air forces would be deployed to FOBs as well and with the short distances and flight times involved, not having mach 2 is not a major factor for JF-17.
3. I am not sure if this is entirely correct. WWII bombers were not flying at Mach speeds when they dropped their nukes over Japan. The lower the flight profile of the mission, the greater the need to get out of the blast radius of course, but again, I don't see that as a real possibility anyways. If anything, with the advent of missile in the subcontinent, the delivery system is not going to be aircraft anyways.
4. I can't speak to what other air forces might need or want, however, as with anything, there are design compromises made and they would know that already. DSI for simpler manufacturing, maintenance for slightly lower speed is a trade-off. But its not the same as not having a 2-seater from the get go.
5. Again, Gripen has different design features as well as requirements, mainly the interception of Soviet bombers over the vast ocean spaces. Again, they are not going to go Mach 2 carrying much in terms of fuel tanks or weapons ... It is also quiet possible that mach 2 for Gripen was not the intention or requirement but just a consequence of its design? Again, can only presume here since we have no idea really of what Saab's intention was or what the requirement was for the Swedes.
Should it apply to JF-17? I would argue it is not worth the slight gain we might see at a great cost as its usefulness is not quiet apparent in our theater of operations.