From WWII to 2021, there have been 33 times a player scored 0.8 GPG (with a minimum of 40 games played). Ten of those players won the Hart. That sounds promising, but nine of them also won the Art Ross (Hull 1966, Esposito 1974, Gretzky in each of 1982, 1983, 1984 and 1985, Lemieux in 1988, 1993 and 1996). The only player who scored 0.8 GPG and won the Hart, without winning the Art Ross, was Brett Hull, who in 1991 finished 2nd in scoring (16 pts ahead of 3rd place).
There have been 9 instances where a player scored 0.8 GPG, and finished between 3rd and 5th in scoring (which is what Matthews is going to do). Not one of them won the Hart. In fact, several of them weren't even finalists.
I appreciate Matthews' goal-scoring this year. It's obviously one of the best goal-scoring performances of the 21st century. It would have been greater still, had he not missed so many games. But over the past 40 years, the Hart correlates much more strongly with overall point production than goals (or assists) in isolation.
And although I agree that Matthews is one of only two players since 1994 to score 0.8 GPG, he's not the only player doing historically significant things this year. Roman Josi is having the highest-scoring season from a defenseman dating back to 1993 (and he's far better defensively than Phil Housley, the last blueliner to top his 93 points). Johnny Gaudreau is the first forward since Wayne Gretzky in 1987 to finish a year +60 (and he's one of two forwards going back to 1994, the other being Jagr, to reach 88 ES points). These are all cherry-picked stats, but none are any less arbitrary than "0.80 GPG, going back to 1994, ignoring Lemieux".
I'm not saying that Matthews can't or won't win the Hart. Just that this particular argument doesn't really tell us anything.