Defense is useless against Falz simply because none of his attacks take that stat into account. All of Falz attacks either deal elemental damage which is reduced by your armor and shields elemental resist stats or they deal set damage which cannot be reduced at all. A good and cheap set up I can think of for Falz is to grab a charge raygun with high hit and charge vulcan with high hit from the shops which become available after you hit around 150. After that try to max out your ATP and ATA with units and a good mag build. Cure Freeze is good for Falz 2 to avoid getting combo killed so a hunt invested in finding one may be worth your time. Primarily, you will be using mechguns on the first two forms and switching between handgun and mechguns on Falz 3, but if he moves to you and you do have a powerful and accurate melee weapon then you can use that as well but you are probably best avoiding melee.