The committee letter process effectively does weed out marginal pre-meds from applying, effectively raising the school’s medical school admission rate. It may also be good for the weeded-out pre-meds, although it may not feel that way to them at the time, since they know earlier that they should switch to plan B due to extremely low probability of success in the expensive and stressful medical school application process.
But it does mean that medical school admission rate at schools with pre-med committees may reflect more on how selective the pre-med committee’s screening process for pre-meds to get a committee endorsement is, rather than other aspects of the school being good or bad for pre-meds.