Exactly, they can detect stealth targets at the same ranges as non-stealth targets, it's a possibility, not an absolute statement. They can lost his advantage.
This is not at all what ExNusquam said. To repeat it in a slightly more direct fashion, the P-18 can detect non-stealth targets at distances of up to about 100 miles. The F-117's stealth features reduced this to 30 miles, and VHF stealth technology has improved substantially since that point.
Fundamentally, stealth works by reducing receiver signal to noise ratio (SNR). The signal returned from the LO aircraft is smaller than the signal from a conventional aircraft under all circumstances. Because you can't pull information from thin air,this means that you always have reduced detection distance against a stealth aircraft, or more precisely, your detection distance is proportional to radar cross section of the target aircraft. No clever processing will let you get around this that won't also increase the range against non-stealth aircraft, as the non-stealth aircraft's SNR will be equal at longer range than the stealth aircraft's.
Remember that there are some parameters in addition to the wavelength.
Importantly, wavelength is the only one that actually lets you change the target cross section. The other parameters are all impacted by the SNR reduction as a result of the reduced RCS, to the point where at range you are unable to differentiate the stealth aircraft from the noise floor. By changing the wavelength, you can change the effective RCS of the target, potentially increasing the receiver SNR.
