For context - there have been two Hart finalists on the same team 19 times in NHL history. Ten of these instances were prior to the 1967-68 expansion (fewer teams, so it was more common for two teammates to be the finalist for any award).
Of the nine that happened after expansion, five of them involved Bobby Orr and Phil Esposito. There have only been two Hart finalists on the same team three times since then - 1982 (Trottier 2nd, Bossy 3rd), 1988 (Fuhr 2nd, Gretzky 3rd), and 2001 (Lemieux 2nd, Jagr 3rd).
Sticking to post 1968 so it's a bit more relevant to larger league - in how many seasons can we truly say the 2 "best" players were teammates? Or even 2 of the top 3 "best" players?
Espo and Orr obviously, and as you say they were finalists together 5x.
Jagr/Lemieux too, but their prime didn't exactly matchup. 1996 should have been but Jagr missed and finished 4th. 2001 they were. 1993 Jagr wasn't good enough yet, 94 & 95 Lemieux didn't really play, 1997 Jagr was injured, and 98-00 Lemieux didn't play. So although they were probably the best 2 players in the league when they played together, they really only had 2 full seasons together, and once they were both top 3, one it was 1st and 4th.
Gretzky was the best player while in Edmonton, but i'm not sure that any of his teammates was the 2nd best player in the league in that stretch. Coffey maybe could have once or twice, but D don't usually get proper hart recognition.
Than you have Crosby/Malkin, among the 2 best players in the league for the past ~12 years. But they never had a single season where they both were on top of the league. The closest is probably 2009, but Crosby was a bit behind pace and him not being a finalist seemed correct. 2008 likely would have been, but Crosby missed ~30 games. I don't think there's a single other season where you can look and truly say "yeah, they're 2 of the best 3 players this season". Malkin either has an off year, or Crosby/Malkin missed time to injury.
So my point is - since the 70s, the only 2 instances I can think of where you could say the 2 "best" players were teammates was Jagr/Lemieux and Crosby/Malkin. And only Jagr/Lemieux were the best "in season", twice. Once they were both finalists (2001), one just barely missed (1996). So McDavid + Drai being in the running for the 2 "best" players this year is a truly rare occurrence. In my opinion - they both deserve to be finalists