I'm sure such a rating number in a horse's last race could be dredged up to suit the distance parameters required, but I'm trying to work out [considering the amount of things during each particular race that would effect individual runners at various distances], what possible use such a rating number could be. Especially taking into account a horse's particular running style, jockey, barrier position and at what track etc. etc. that will all influence the outcome of a race for each horse in it and what position it was in at various distances in a race.

For instance, at the 800m and the 400m a winning backmarker [eventual winner of race] will be about last and a losing leader [eventual last] will be about 1st.
In the last 400m their positions will go through a rapid transformation covering almost every position in the field from first to last. The leader will be covering them as it looses ground and the backmarker will be covering them as it gains ground. In fact this could all happen within the last 300m, 200m or even the last 100m. First to last and last to first.

There might be some use for such a rating figure for on-pace grinders [only], but even that would be of iffy use.

Of far better possible use which could be give a rating number, would be sectional times, but even these figures [suitable to USA dirt tracks and Aust. trots] have debatable worth on Australian race tracks, considering very few of them have the technology involved to gather that info. for a start and also the widely diverse layout of our tracks and movable barriers.