Better weapon but still downsides

I know title is confusing so let me explain it like that:

I have courage hammer 3* (+2% HP and +3% Attack is text green i dont know why?) on my DivineSpirit and when I try to replace it with better Night Blade 4* even tho it has more HP and Attack% on it's perk on whatever you call it. I still get like -32 attack. Why is that? Is perk on weapon relevant like that? How do I know which hero has cons and which has pros of a certain weapon? Any explanation much appreciated guys xD