5e rules is plain dumb, dead lifting something is going to be harder than straight pushing or pulling something. It says a average person is str 10 btw so -8 will be lacking in that department.
Well, I did admit, 5e is crazy in many areas. 10X30=300 lbs lifting ability? I still think that's straight up nuts and unbelievable for a Strength 10 average person. Even if average is a farmer, 300 lbs is heavy. An average person trying to lift 300 lbs and putting all they have into it would be an amazing feat. I have a REAL hard time with rules like that.