M:I 2 had pretty standard summer legs for 2000
Compare that to Gladiator's legs, which opened only a few weeks before.
And M:I 2 had the second lowest #1 WW gross of any film within 5 years in either direction.
2005 Harry Potter and the Goblet of Fire $896.9
2004 Shrek 2 $919.8
2003 The Lord of the Rings: The Return of the King $1,119.1
2002 The Lord of the Rings: The Two Towers $923.3
2001 Harry Potter and the Sorcerer's Stone $974.8
2000 Mission: Impossible II $546.4
1999 Star Wars: Episode I - The Phantom Menace $983.6
1998 Armageddon $553.7
1997 Titanic $2,128.9
1996 Independence Day $817.4
1995 Toy Story $373.6
It was still a big success, but it wasn't a monster like the hits in the years around it.