Playing notes on bass that somebody else created makes you a musician... It doesn’t make you a genius. The person who created the notes, Brian Wilson, is the genius. Some others added lyrics and those are important too... But Brian Wilson was the genius behind the Beach Boys and the documentary makes that more than clear. Others were along for the ride, but he was master of that circus
The Wrecking Crew was a great group of very talented studio musicians who played his music very well. Period!
Unless it was a charted-out movie score, the studio musicians had a lot of flexibility to come up with their own lines and riffs.