They could make chainsaws lose durability significantly faster when attacking zombies but have them actually deal a decent amount of damage to zombies.
or they could make it so they have a jamming mechanic where they get clogged with flesh and it takes several seconds to un-jam them. So they do a lot of damage but randomly get jammed for like 5 or so seconds making them a bit risky to use.
Also, I agree that the gear crafting system is mostly useless since you will receive/find gear that is better than what you can make most of the time. They probably should lower the quality level of the rewards traders offer and they should add unique bonuses that can only be found on gear that you craft. For example you could craft a spear with a built in attack speed bonus. Or a higher chance to dismember a zombie, or knockdown, or knock back, etc.