Your numbers are slightly wrong. If I've calculated correctly, we picked up 29 points from a possible 42 against the bottom 7 (of the final table)
It wasn't so bad in the first half of the season:
Record vs top 6: Won 2, drew 1, lost 2 - Pts 7/15
Record vs 7-13: Won 6, drew 1 - Pts 19/21
Record vs 14-20: Won 5, drew 1, lost 1 - Pts 16/21
2nd half:
Record vs top 6: Won 4, lost 1 - Pts 12/15
Record vs 7-13: Won 4, drew 2, lost 1 - Pts 14/21
Record vs 14-20: Won 4, drew 1, lost 2 - Pts 13/21
Our performances against the mid-table teams dropped over the course of the season, too. I think the comfort of being clear of Liverpool/Spurs and our record against our rivals meant that we dropped off a little against everyone else, especially when the league was gone.