Prize-money alone not an indicator of class. For example, a horse called abaridy won a big race on a wet track- heaps of prize-money, yet won very few races thereafter- I know, to my cost. Van Der Hum won a fortune- few would call him a class horse - you need to consider consistency as well. E.g how many wins out of how many starts. Class horses a) Win high percentage of starts AND
b) Place with great regularity AND
c) Win stakes or w.f.a regularly
We can all recognise some class horses e.g Northerly, Sunline etc. Relative class in weaker fields is a valid idea but harder to define.