While that's true that he is a safe choice, he's never the best choice.
Every character has a matchup that is harder or just as hard as Meta Knight (usually Snake, sometimes other Top or High Tiers).
There might be a handful of exceptions, but I could only think of one (R.O.B., and even there I'm not sure considering Zero Suit Samus' Footstool combo and whatnot).
So if Meta Knight is gone, for most viable characters (meaning S through C Tier), a slightly disadvantaged matchup is gone. While he is common, hardly any character has so much trouble against him - I can count these viable who do characters on one hand.
They will still have harder matchups, and since the Meta Knight players who continue to play will simply switch to other Top or High Tiers (logically thinking, I doubt good players will switch to Low Tiers, really), there is only an increase of Snakes, Warios, Falcos and other Top/High Tiers. Which means that if you play Mr. Game & Watch or Donkey Kong (two characters who actually do okay to well to Meta Knight), chances of running into a Snake or Dedede respectively have become higher than before.
There will neither be an increase of Low or Mid Tier mains placing - these characters aren't viable anyway.
The only thing that'll happen is that the top placings go either all to one character (Snake is suspected to become the next dominating character, here), or they split up on S Tier (which is a bit more reasonable).