T-50 is only marginally reduced from F-16 in capability, it's also half the cost and is being considered for T-X. The USAF has already decided it doesn't want anymore F-16s, it's not going to suddenly decide "oh well we want them now".
The USAF should actually procure a twentieth what it ordered, about 60-70 airframes. The rest can be filled by T-50s or M-346s or some other super trainer aircraft. Given that the West is only going to be conducting COIN operations in the foreseeable future, this would be an exceptional fiscal decision. It gives the USAF a stealth capability without sacrificing current inventory of aircraft.
Strike radius compared to an F-15E with drop tanks, which is what F-35 is replacing. Don't forget that the F-35 has no drop tanks, which will limit its range when it is required to carry an external payload.
Do you know F-35's intended role? It doesn't sound like you do.
The USN is currently on track to order 36 F-35Cs, if any. It intends to use USMC squadrons on the super carriers (much like it has for several decades now, shocking!) instead of naval squadrons. It would prefer to not have to buy any F-35s and instead acquire large quantities of (comparatively) cheap F/A-18E/Fs, EA-18s, and X-47s.
"So low", hardly. It was a deliberate decision. It's called O-S and weapon system cost. F-35 isn't so great as to replace F-15 and F-16 on a 3:1 basis. It's 2:1 at best, and even then there's something to be said about actual inventory numbers when assuming attrition rates. The USN has taken the latter to heart, and given that it will be at the forefront in any Pacific war with the PRC it has chosen to not acquire F-35 in favour of larger numbers of legacy aircraft.
This is, again, a very sound decision. F-35's passive stealth will likely be significant compromised as future very low band radar systems are developed by the former Eastern Bloc, and in that case it will be no superior in RCS than Stuper Hornet and other current carrier aircraft.
F-15Es will be retired ten years later to be replaced by F-35s, unfortunately.http://www.airpower.maxwell.af.mil/digi ... trucha.pdf
This is a very good article about the whole thing. While I disagree with the author's assertion that F-35 should be canceled (such a move would leave the West without a highly modern aircraft for some time as the current fleets age), there are still exceptional alternatives especially for replacing F-16 and T-38, which forms the bulk of the Western air forces.
T-50 would be cheaper than current late model F-16s, provide a similar capability in terms of range, reliability, and weapons payload, and more importantly could perform functions across a broad spectrum of operations. COIN, LIFT, and air superiority are all roles that T-50 can do quite well. Since the USAF is not interested in acquiring modernised F-16s, this is the best option for them if they wish to retain a sizable air fleet.
While an all F-35 air force is appealing from the standpoint of sheer capability, it comes at a significant cost (figuratively and literally) that will reduce the USAF's capability for global operations in the future. The most realistic outcome is that many of the aircraft will never see combat in high intensity operations and be used simply for police operations like Irak and Afghanistan, where something like T-X might perform equally well.
When the threat air defence is MANPADS and machine guns, it doesn't really matter if you're flying a $160m stealth jet or a $30m trainer.