A guy who hasn't sniffed the playoffs has no business in this conversation. I don't think McDavid should be automatically be assumed #1 either. Kuch, Mack and Drai have all been just as good if not better the last couple years. The top 4 is pretty unanimous right now, but extremely close between them.
Why not though? It's obvious if there was a poll asking whose the best player McDavid 100% wins by a huge majority. Unanimous? No, very few things are, but still it's pretty obvious. Asking who #2 is is the much more interesting topic.
I agree with your top 4 (tempted to lump Crosby in there too - but i understand questions since injuries really impeded him last year). The one thing McDavid has on all of those guys though is:
Kucherov, career year, way above everyone else....except McDavid, who hung with him. Finished second, but quite close in scoring race. Mack and Drai much farther back.
Drai, career year, way above everyone else....except McDavid, who hung with him. Finished second, but quite close in scoring. Mack and Kuch further back
McDavid wins Art Ross and probably sweeps award in 2018, but his team misses playoffs, so he doesn't get votes. Still above all 3 other guys in scoring race.
McDavid is no Gretzky nor Lemieux where he'll sweep the awards and scoring race every year. But others will have ups and downs - and he's always there at the top. That makes him #1 until proven otherwise.
I think if you have Drai repeat last year's success (again topping McDavid), or Kucherov repeating his 2019 season (and again topping McDavid) - both would be in conversation for #1. But until then, it's McDavid.