Calvin, and the Bible, did NOT state that humans are always evil and wicked sinners, but tha we canot ever do anythingby and in ourselves to merit salvation!
All Good things are God given that's no problem. I would push it even further to say you can't even sneeze without God's grace involved. The error however is accept mankind as naturally separated from God. The STANDARD of man, the example of a man is Jesus Christ. When we look at Jesus there is no "SIN NATURE". To attribute mankind as having "sin nature" would also mean Jesus Christ is not 100% human.
Nature is God determined and is GOOD. Sin is not the creator nor can it dictate nature.
If we take a stone wheel and corrupt it with a hammer it will remain a wheel to an extent but the moment it ceases to be round its not even longer a wheel the corruption has destroyed it.
Mankind's roundness if you will is the GOOD IMAGE OF GOD. The moment you say its all good is gone there is no longer a man there. There is nothing salvable its GONE there is no good.
John 3
16“For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life.
In situation where there is NO GOOD to be found in the person, THEY ARE PERISHED, There cant be a situation for preventing any perishing if you already start with them dead. Jesus' statement here would be a lie.
You can't promise no one will ever get wet when at the start you already have them in the pool.