I agree that Brian Wilson was not a bass virtuoso. But.......I saw a Carol Kaye interview with her talking about playing bass in the studio for the Beach Boys. She said that Brian had all the bass lines written out on paper and she played note for note in most cases.
Brian is pretty sharp! Live performances, he used thumb. Worked.
(I am nobody.) At age 15 (1967, I started playing bass with a guitar pick. Then, the 2 finger way started becoming more popular in the 60s plus, it looked cool. I was able to master it. Then, around the early 2000s, I saw a video of Jerry Scheff knocking off unbelievable bass lines with Elvis live with the TCB Band, using only his index finger. (I was already aware of Jamerson's one finger style.) So, early 2000s I switched from 2 fingers to index only for about 98% of my plucking. Sometimes I use 2 fingers for tricky little things. I can actually pluck repetitious notes faster with one finger than with two. But that is just me.
Anyway..............