Mech build question

With those numbers I'd agree that hammer is stronger, but I have never been in a situation where it actually made a difference.
When both attacks kill a monster in the same amount of hits consistently, I'd choose the more spammable of the two. If it's at the point where the increase in damage gives a higher rate of 1-hit kills, I'd of course choose the harder hitter. The latter has just never happened.

But I could just as well ask why people would want to max healbot instead of leaving it at 18. Even after Chaos it's only a 4% difference.

Why max a useless skill when you can max an only somewhat useless skill?