In particular we assume that there aren't, or won't be, technical counters to the low observability features of the F-35 in the relatively near future.

If you're using radio waves, then there really won't be any counters at all (from a realistic standpoint).

Things like linked radars would work in theory, but those concepts completely break down when you introduce hundreds or even thousands of decoy drones (like the MALD). This drone can mimic the radar signatures of most aircraft in the US's inventory, from a B-52 to an F-22. It is undoubtedly one of the most underrated pieces of equipment related to air power in the US military's inventory. Most people don't even know that it exists.

So even if you did find a radar-based counter to stealth, it wouldn't matter. You'd be wasting all of your ammo on targets that you think are real. And reloading/resupplying advanced SAM sites isn't as quick or easy as reloading a rifle.

Never mind the fact that it's literally impossible to use radio waves against a stealth aircraft with the same effectiveness against non-stealth aircraft. The scientific laws dealing with radio wave refraction and reflection are completely unchanging, and cannot be broken (no matter what, and that also includes future radar technology dealing with radio waves). You might get some stealth aircraft shot down, but it will never be anywhere close to the effectiveness against conventional aircraft.

Another technology might exist in the future, but it will be something completely unrelated to our current usage of radar.

As for IRST and BVR IR missiles, that's an even worse proposition against stealth aircraft (even moreso than X-band radar). Current Russian OLS IRST's have a realistic range of maybe 10 miles in average weather, which is just truly shitty (their numbers represent absolute maximum, which isn't not normal).