This. Whilst the hypothesis is plausible, there are plenty of other reasons for diminishing returns to growth in more developed states which are difficult to distinguish.

Skimming through the short paper its basic regression attempts to control for differences in development by including variables for other development indicators, but it's a very small sample skewed by Korea, Japan and especially autocratic-era Taiwan reporting low levels of [formally qualified] lawyers. The authors even comment they 'would be surprised if someone could not come up with a specification to support the opposite conclusion'!