That is definitely an issue that is out there. Sadly cheap builders try and get away with a single return per floor in a house which is simply not enough. My point is mostly that forced air versus hydronic isn't what causes a difference in dryness of air. It largely comes down to the quality of the install of each and the tightness of the home. Hydronic is typically more expensive and tends to be found it better built homes. My house is an exception to that rule though, I am still working on sealing up air leaks from where all the pipes ran for our baseboard heat.