So in many ways, the U.S. Army really needs that MML or MSL to carry and launch the AIM-9X for about a 20+ mile range or else risk being an all-Stinger mobile SAM force still.
The US is still in a world of hurt regarding Air Defense. You've got nothing between light, short range IR guided SAM's (consisting of decades old Stingers) and heavy, fixed Patriot batteries (which one assumes would be a priority target if we ever fight against a peer). Adding optically guided MG's or Hellfires isn't going to change anything. A Hellfire, which was designed to target nothing moving faster than a tank, has little ability to take down a fast jet or an agile UAV. Compare that to the layered defenses that the "bad guys" have. The funny thing is that the US actually already has a very effective, radar guided, medium range SAM deployed in service. Apparently though, this system will never leave the confines of the USA.
Yes, the NASAM at fixed locations, which isn't USA made. And agreed, the USA is woefully inadequate in SAM defense because it relied on the USAF. One can arm helicopters with Stingers and Sidewinders as an added defense.
I think the USA made a mistake in adopting the upgraded Patriot PAC-3s trailer launchers and not the MEADS system. The Army concluded that since it already has the Patriot components, it will keep upgrading them, but current Patriot radar can't see 360-degrees like MEADS. The Army is working to replace the Patriot radar with one that covers 360-degrees, but still it takes a long time to set the Patriot launcher in place. MEADS was Internationally developed with USA funding and help because Patriot wasn't light and mobile enough. Only the USA didn't adopt it.
Then there's SLAMRAAM which was tested and didn't get anywhere. And USMC LAV-AD that apparently got scrapped from the books and no one ones why.
The US Navy has RIM-162 ESSM that goes out to 50+KM at Mach 4+, but at about $1 million per missile, I doubt the US Army might field it.
I think the best approach for the USA would be to buy all the IDF SAM types from Arrow to David's Sling to Iron Dome and then make THAAD into THAAD-ER. THAAD-ER has much better performance parameters and range than original THAAD.