The problem with stealth aircraft isn't finding a missile that can hit them. It's getting a reliable, targetable lock on them. You can detect stealth aircraft with low frequency radar, but you get a very poor quality return. Low frequency doesn't just make stealth aircraft more visible, it makes *everything* in the atmosphere more visible, including water vapour.
A good example of what it takes to shoot down a stealth aircraft with a low frequency radar can be seen in the one time it was accomplished, by the Serbs during the Kosovo conflict. The airplane flew right over their position almost every day. Even with it right overhead, they still couldn't target it most of the time. The time that they finally got it, it was right overhead and had its bomb bay doors open, significantly increasing its visibility.
And this was with an old generation of stealth aircraft.
No country in the world wants to have this much difficulty hitting their adversaries targets. Is the problem solveable? Probably eventually. Is it solved now? Very doubtful. As good evidence to that effect, look at how much money Russia has been throwing into their antiaircraft systems - first modernizing the S-300, then introducing the S-400, and now developing the S-500. Much of Russia's military struggles for funding (look at the sad state of their only aircraft carrier, for example, or their struggle to bring tanks like the Armata or planes like the MiG-35 into full production), but air defense gets tons of money. If they had actually solved the stealth problem and felt that they could reliably shoot down US stealth aircraft, they wouldn't be focusing so heavily on it.