PG - I think you might have left out some valid info on who else is also looking at kids - and the relative numbers they each see in a given season and perhaps on a repeat basis. I don't know your numbers, but can only assume that your counts are a multiple of others - 10x+ for all but a few. I'm sure there are some regional differences (PBR's coverage comes to mind even though I personally am not familiar with them), but for the "typical" D1 - not counting all the Top 100 listings - PG has got to have by far the broadest and deepest coverage. Not saying this is the best option for every kid (some can/should work on exposure to smaller, targeted lists), but I think your answer on what makes PG the authority is lacking some necessary statistical support.
Has the OP provided any basic stats on his 2017 pitcher? Not sure he has gotten a really good answer yet due to lack of some necessary details.