Not at all. They are many times more qualified than any of us. Yet, even with those extra qualifications and additional information including access to medicals and face-to-face interviews nobody knows for certain how a draftee is going to work out. Using all of the information available to them they are all making their best educated "guess" of the eventual success of the selected prospect. It is absolutely an inexact science.

An extensive study done in 2015 on all drafts picks (non-kickers) between 2005 and 2014 showed that only 25.5% of all drafted players became starters for at least half of their careers. It also broke it down between rounds taken and position. The success rate (starting) of DL, RB, and WR picked in the first round is only 58%. QB's are only slightly better at 63%.

Here's a nice summary:

Historic Success Chart

The numbers show us the following outline for finding consistent starters:

1st Round - OL (83%) LB (70%) TE (67%) DB (64%) QB (63%) WR (58%) RB (58%) DL (58%)

2nd Round - OL (70%) LB (55%) TE (50%) WR (49%) DB (46%) QB (27%) DL (26%) RB (25%)

3rd Round - OL (40%) TE (39%) LB (34%) DL (27%) WR (25%) DB (24%) QB (17%) RB (16%)

4th Round - DL (37%) TE (33%) OL (29%) LB (16%) WR(12%) DB (11%) RB (11%) QB (8%)

5th Round - TE (32%) DB (17%) WR (16%) OL (16%) DL (13%) RB (9%) LB (4%) QB (0%)

6th Round - TE (26%) OL (16%) DL (13%) WR (9%) DB (8%) RB (6%) LB (5%) QB (0%)

7th Round - DB (11%) OL (9%) QB (6%) WR (5%) DL (3%) LB (2%) RB (0%) TE (0%)

Of note are the defensive line draftees. Outside of the fourth round their success rates are dramatically low.