Yeah, I'm not imagining that .447 GOAT mark is sustainable, but I think the sample is probably big enough to start thinking of Cook as an elite shooter, given all the other indicators:
.437 3fg last year in the G-league (in 190 attempts, 6.6 per game, 28 usg)
.950 ft last year in the G-league (114-120!!!)
.395 3fg (258 attempts) and .891 ft (110 attempts) his last year at Duke
Post Jarrett Jack, the Myers-era Warriors have typically shied away from having a "Steph lite" on the roster, in favor of 6'-7" point forwards like Andre and Shaun who can back Steph up but also play alongside him without compromising the D. With Steph potentially getting a bit more fragile as he enters his 30s, and Andre and Shaun getting old (and Shaun a likely luxury tax casualty next Summer), I think the shooting and overall play of Cook has made them rethink that approach. He came up huge for them in the last 25-30 games last season when Steph went down with the MCL, and so far this year seems to be picking up right where he left off (20.3 pts per 36 on .639 true shooting in his 110 minutes).
Obviously he gives away a ton on D relative to Andre and Shaun (presumably why Kerr played him so sparingly in last year's playoffs) but he brings floor spacing on O that those guys lack, allowing them to play a Steph-like offense when Steph sits. Kerr doesn't like to stagger Steph and KD's minutes too much, and the Ws have had serious offensive issues with "Klay-as-primary-option" units they run out when they sit. Cook (along with that DeMarcus guy, when/if he gets healthy) helps fill that gap.
Anyway, blah blah. Fwiw, here's #7-10 in career 3fg% among active players:
7. Morrow .417
8. Kennard .416
9. Hield .415
10. Redick .414
Four Warriors and five Dookies in the Top 10.