A few things:
What major program has QB's looking pretty good with less talent around them? Michigan hasn't had a legitimately good QB since Harblow took over and he was supposed to be a QB guru who took Andrew Luck to the next level. Florida may (keyword MAY) have finally found something in Kyle Trask, but prior to that, they've had nothing but mediocre QB play since Tebow graduated. Look at UGA since Stafford left in '09. Or hell, take away the one freak year from Burrow in '19, LSU's QB play has been mediocre at best since the days of Matt Flynn and they've had some ridiculous receiver talent. USC has consistently some of the highest end receiver talent, but they haven't had a QB who has consistently been really good since Captain Butt-Fumble. Darnold took the world by surprise in '16, but everybody caught on to his game in '17 and his stats suffered. Remains to be seen with Slovis, but my guess is that he won't catch the CFB world napping a second time around.
The reality is that there are very few truly elite QB's who can transcend the talent around them. Most of the QB's at major programs are solid to good, and are amplified or diminished by the talent around them.
Book is a solid QB, but let's be real, the receiving talent is not where it needs to be. McKinley and Skowronek are solid depth pieces, but they wouldn't start at any major program. Hell, put them on Ohio State, Clemson or Bama's roster, they're never seeing any meaningful snaps.
Book is hesitant to throw and a big reason why I think that is is because he doesn't trust his receivers' ability. I can't say I blame him given what we saw from McKinley on Saturday. It's why Austin and Lenzy need to return in a full capacity IMMEDIATELY.