As RBR loses more points to Ferrari in the battle for P2 in the WCC and VER is cruising to a title win, this seems relevant.
The winning WDC driver was not in the WCC team in 1958, 1973, 1976, 1981, 1982, 1983, 1986, 1994, 1999, 2008, 2009, and 2021.
Let's work backwards. In these years, the WDC driver's team was P2 in the WCC.
2021, VER, Merc WCC champ.
2009, the Brawn year.
2008, McL would have won, but Spygate.
1999, Schumi breaks his leg.
1994, Senna dies and Hill carries Williams to the WCC.
1986, Williams wins WCC, Piquet and Mansell give the WDC to Prost.
1981, Piquet wins the WDC, Reutemman and Jones are 2nd and 3rd in WDC by 1 and 4 points, respectively, Hector Rebarque sucks for Brabham.
1976, Lauda-Hunt.
1973, Cevert dies before the last race, Tyrrell does not race, Lotus had one point advantage going into it, wins the WCC.
1958, Vanwall and Ferrari tie on points, Moss and Brooks are P2 and P3 to Hawthorn by 1 and 18 points (Jesus, Tony...). The rules however... One driver can score points, the FL lap point does not count to the WCC, Indy 500 does not count to the WCC, only 6 scores can be counted for the WCC. It was a glorious mess, honestly, Vanwall won the WCC by 8 points. It was not even called the WCC, it was the International Cup of F1 Manufacturers.
So, like everything else that is bizarre in F1 leads to, the answer is obviously 1982 (and 83).
Williams was 4th in the WCC while winning the WDC with Rosberg (with 44 points). The WCC winner was Ferrari with 75, and Williams finished with 58 pts courtesy of Mario Andretti (3 races, 4 pts), Derek Daly (15 races, 8 pts), and Carlos Reutemann (2 races, 6 pts)
Worth pointing out, obviously, that Ferrari lost BOTH starting drivers during the season, so yeah.
Then it happened AGAIN in 1983, with Brabham scoring 72 pts to Ferrari's 89 to finish 3rd, while Piquet won the title with 59 points and the #2 driver was Ricardo Patrese with 13 points and 9th in the WDC.
This has no excuse, Patrese was simply horrendous with a very good car, in a more spread out season.
Now the true question is this:
How sucky is PER? We cannot compare it with 82 because that was a revolving door in the #2 car, so we can only look at 83.
Patrese scored 18% of the teams points that year and the team scored 80.89% of what the WCC winner got.
So far, PER has scored 29% of the teams' points, while RBR has 89.32% of McL's points.
So PER is not historically terrible as a #2 driver, but man he is garbage.
RBR lost P2 in the WCC for being insane enough to trust PER would not suck this season as he did last season, and we get to watch another historical year in F1.