Bit of an odd jump 3 to 4; ie why the inclusion 'leave the house several times...' ?
I agree. Leaving home is more a social measure than a health measure. Some people will do anything to get out of the house once in a while even if they are very ill, while others are content to stay home. Also, people who have social and physical support to drive, push wheelchairs, and the like are more likely to get out of the house than those with no social support, regardless of severity level. There were years that I got out of the house a couple times a week because I lived with family members who could help. Since I could neither drive nor walk more than 10 yards at the time, if I had been living alone I'd have been completely housebound.
IMO, there's no such thing as a GOOD activity scale. There are too many variables. Some scales are better than others, but no simple scale can capture our experience.