You have only repeated the statement of those, who claim that it is no problem to remove on part of a designed system and that it could still perform the function, eventhough a part of the system is missing, with some few software adjustments. But why is this possible? And why did the designers of SPY-3/4 pair, which thought otherwise, are wrong? Also the next generation, AMDR (SPY-6), will be a combination of antenna, again a X band/S band pair as SPY-3/4 (
https://en.wikipedia.org/wiki/AN/SPY-6). Therefore the radar designers apparently still think that for full function two different bands (sets of wavelengths) are necessary. As do the designers of radars for other navies. And these bands have different physical characteristics.
If you read the different Wikipedia articles, you will find that most modern radars have more range and for those the range is described in much more detail, including references, which are unfortunately completely lacking for SPY-3 on Wikipedia. There is unfortunately also no information about the characteristics of SPY-4.
But there is information on Wikipedia that SPY-3 was designed to guide SM-2 and make SPG-62 or similar fire control radars not longer necessary, i.e. a SPY-3 ship does not need additional illuminator radars.
In general, longer wavelengths appear to be also better for detection of stealth objects a longer distance, which again would require longer wavelengths than the X band of SPY-3. We talking about a time with massively increasing range of anti-ship missiles (more than 200 miles for the new Russian ones!), but for sure the radar horizon and the over-the-horizon capacity would be relevant here. Sure, purely for defence horizon search would be sufficient, but regarding the attack role, this is a different topic. Unfortunately this is a topic not described in any detail for most radars in the Wikipedia articles. The height of the missile reached directly after launch (before it goes into low level flight) would also play a role here, if range could be relevant - I could not find any detailed information about that.
But again: if something is designed to work as pairs, I assume that it causes problems, if one part is removed and still the same function should be available. That is usually either causing disaster - or amazing technological progress. But disaster or at least a massively inferior technology, is more likely.