I think one has to have experience of both longer and shorter LGFs in MRBs to conclusively say either way!
I think the question might also totally depend on crown height - as fatter arrows might give more fire but that would be totally lost in a stone with a low crown?
It seems that some proportions work better with short lgf. This is a DiamCalc question ...
Some looks found among older RBC are unexpectedly nice - e.g. 70%-ish lgf & larger tables, look like a checkerboard of sorts (great contrast, very bright !).
Depends on the combo, some combos work better with longer lgf% and some it does not matter much as far as performance but gives a different look.
Basically the deeper the pavilion or shallower the pavilion the longer the lgf% should be(closer to 80% and sometimes over).
It also depends on how you define thinner and thicker.
Many times I have seen ones in the normal range of 75-80 called thin or thick but technically the are normal for a mrb despite the difference in look.