Did Wayne Gretzky's scoring get marginalized just because Mario Lemieux turned up a few years later? No, it didn't.
What matters are the general circumstances.
Was Selanne scoring 76 goals in 92/93 somehow less special because Mogilny did it as well? No, it wasn't. Though it certainly makes a difference whether you score 70+ when no one has touched that mark in a while, or when the league is on a five year streak of players topping 70 goals that includes even two 80 goal seasons.
If two of the best players ever happen to be around at roughly the same time, it doesn't make them less special than if they had been around at seperate times. Just like two players accomplishing a rare feat at the same time doesn't somehow turn it into a lesser feat if everyone else is clearly behind.
If there are two instances of something happening over a ten year span, then it doesn't matter whether they are years apart or happening at the same time. Two players accomplishing something that hasn't happened in ages is a great feat. Now, if you see multiple 100 assist seasons over the next few years, then yes, it would become less special.
Last season two players topped 80 assists, two topped 70, and four stood at 69, all of which missed enough games to think they probably would have reached 70 if they had played them all. So basically 8 players pacing for 70+ assists (not counting anyone who missed a lot of games).
This season two players reached 100, one topped 80, another two topped 70, and unless something big happens, Makar is the only one who could still reach 70 as well. Which means only five players were pacing at 70+ assists, meaning it's not like assist totals have completely exploded among the assist-leaders.
McDavid topping 150 points when only his teammate cleared 115 is obviously more special than Bernie Nicholls reaching 150 while "just" being 4th in scoring and 49 points behind the leader. That's were you can make a clear distinction, but not with two players reaching 100 assists at the same time. Not as long as that starts to become a regular occurance.