"1.The best people enter fields that accurately measure their quality. Fields that measure quality poorly attract low quality."

I would edit it thus:

A- "Fields that measure quality poorly retain low quality, and repel The Best People." (The Best People will get fed up and leave)

and a related:

B- "People of varying quality enter fields that reflect a lot of different things, low on the list of which is how that field measures quality. High on the list would be how that field is compensated." (in all the variations of "compensation": monetary, social status, secondary characteristics, ease of entry, ease of continuation, ease of exit strategy, duration to exit, do the chicks/men dig it, do the parents approve, etc....). There is a huge incentive to enter a field that measure quality poorly, but compensates the entrant well.

(this is somewhat related to the "public school teachers" comment already made, but I thought that reply veered into something else)