Longer runways and using wet thrust to launch with bigger payloads all mean you would be sacrificing range, as well as potential top speed.
Yep, and that was mostly to illustrate that it's easier to potentially allow an aircraft with underpowered engines to get airborne with an intended payload (with less consequences to achieve it and without excessively high consequences if it is not achieved), and harder for an aircraft with underpowered engines to reach a desired speed with an intended payload in an egress situation when pursued by the opfor (and with more significant consequences to achieve a desired egress speed, and with the loss of the aircraft being the high consequence if a desired speed is not achieved).
Of course there's various ways to mitigate things to achieve an acceptable payload and acceptable speed for an aircraft with less powerful engines as well -- just change its doctrine and SOP in use.
EDIT: The points you elaborated on about missing top speed and its potential perils is precisely why I'm skeptical they could pull this off with less than adequate engines.
Standoff weapons + change in SOP, such as using such bombers against slightly less well defended targets or maybe operating alongside dedicated EW or fighter escort or whatever.
I'm not trying to mitigate the importance of stand off strikes. As I said in my edit, my skepticism is more rooted in redundancy of capabilities. They don't necessarily need a stealthy supersonic striker to achieve those kinds of stand off capabilities. Stealth+supersonic is very very nice to have, but it's less of a necessity, and, furthermore, the value of that combination rests on the point about engines, which suggests going with suboptimal engines wouldn't be an option. The point about JH-7s and KD-88s gets to that point.
Hmmm it depends on what the range of the weapons are, and what the distance to the target is.
For instance, if they conceivably develop a 300km class stand off cruise missile ala JSM, they will still have to have an aircraft that can travel to 300km away from the target in an undetected/stealthy manner to reduce warning time for the enemy, and if the target is 800km away, then that's a 500km combat radius assuming you launch your missile at the edge of its envelope, and that is 500km where a JH-7/A or J-16 won't cut it as they'll be detected well before they get within launch range anyway (and intercepted ofc)
OTOH, if one has a 3000km class cruise missile like CJ-10 and you're trying to hit a target 800km away, then you obviously won't need your launch platform to leave your own airspace at all (one doesn't even necessarily need an aerial launch platform to begin with!) -- but there are obviously still missions where a bomber+stand off weapon is preferred compared to only long range surface launched cruise missile (both of which would be very useful in high intensity scenarios), and obviously there are also situations where bomber+unpowered PGM is useful as well, but I think most of those are relegated to lower intensity conflicts.
As for strikes behind enemy lines, I was actually thinking fixed targets (since I think in a full blown conflict the US would need to secure land for logistics and supply chains to sustain any fighting effort).
I think that regardless of whether the targets are fixed or mobile, in any high intensity conflict that China gets into, it would be preferable to use stand off weapons, simply because of how formidable the enemy will be. China cannot guarantee successful air superiority or anything near complete SEAD when conducting offensive strikes against the kind of foes they're looking to face, especially behind enemy lines, so any way in which they can reduce the risk to an aerial launch platform should be considered, so long as it does not compromise the mission's core objectives.
