Well that last part is a bit hasty. I would agree that phase change systems are already well explored and it is true that high humidity (and temperatures) make dehumidification much more efficient. But it is also true that dehumidifiers in fact do work and can extact moisure from the air in significant quantities.

The scammy stuff in my opinion are the ones that claim to work with no energy input or passive water collectors. Those are gimmicks that only work in ideal circumstances and produce very little moisture and still require significant maintenance.

On the other hand, powering heavy duty compressors with renewable energy is a very different story. In this case, there is no question that the technology is effective and very real in the here and now. The catch in this latter case is the cost and that would include things like, for instance, tariffs that artificially increase those costs. I would say there is a big leap from something being too expensive in the current market snapshot to "This is not a viable solution and will never be." That's too big of a jump.

Moreover, a dehumidifier isn't engineered for maximzing water production, it is engineered to reduce humidity and it happens to create water as a waste product in this process. Simply looking at a compressor powered dehumidifier and saying that it is impractical for producing water at a large scale is a small-minded way of looking at the situation. That device is not intended for water production, it merely suggests an interesting possiblity.

With a large compressor and a very large condensor array coupled with dessicants there is no question that water can be extracted from desert air much like the scenario shown in in the Star Wars movies on the planet Tatooine. Making such systems affordable is a serious challenge but writing it off as completely impractical is going too far. Anyone with a dehumidifier can see that it's possible.