B737-800 First Officer reported vision problems caused by the hydrophobic coating on the windscreens caused misjudgments and an excessive sink rate during landing. A hard landing was entered into the log book for maintenance action.

Narrative

The Company has put out several communications lately about the hydrophobic coating on the windshields and I remain unsatisfied with their explanation and continue to believe that their unwillingness to treat the windshields poses a serious and unnecessary risk to the Safety of our operation. My last flight highlighted the issues. Landing on XL in ZZZ; the ATIS was reporting +TSRA and 2 1/2 miles visibility. We were cleared for the ILS Runway XR. At minimums; the Pilot Flying (PF) announced 'landing'. While the runway was somewhat distorted by the rain piling up on the windshield; neither of us felt it was bad enough to call for the go-around. Here lies the problem with not treating the windshields with a hydrophobic coating. The crew is lulled into a false sense of security to continue the landing. However; I believe; based on experience; that the Pilot's depth perception is severely and unknowingly impaired by the distorted view.This was just what we experienced. Just before touchdown; we got a Sink Rate Aural Warning. It was too late in the flare to initiate a go-around; as we touched down almost immediately after the warning. As you might imagine; it was a hard landing. What was unnerving to us both was that neither of us had the slightest inclination that the aircraft was sinking. I attribute this to our distorted view through the windshield. We felt that we had adequate visual reference to continue the landing; but clearly; we unknowingly did not. I have seen this happen other times as well and always in heavy rain. I happen to know that other airlines maintain their windshields better than we do. When I observed (other carrier) land immediately after us in the same conditions; they had a much more normal touchdown. I have worked for operators; in the past; who maintained the hydrophobic coating and never had any issues landing in heavy rain. We also didn't even have windshield wipers on our aircraft. I strongly believe Company is assuming unnecessary risk by choosing to operate this way.