I believe CP is a weight/class rating for it's career and assumed that $ was an average prize money rating. The ratings for a particular runner may be adjusted depending on it's opposition's ratings. Just guessing.

For the last 20 months or so, the horse with the highest CP rating produces the best ROI of all the criteria. The $ rating has the same strike rate but worse ROI.

Prizemoney ratings seem to be overbet, generally, whether it be consciously or not. The horse with the 2nd highest $ rating has a better ROI than the 1st. This may be the same for API - I don't have it in my database - maybe someone else could check.