That is not entirely true. Lets analyse a real example.
Last night i played one wizard in a group of 4 players level 3 (Wizard, Paladin, Rogue, Cleric). We had 3 encounters.
On the first one we faced 2 bugbears, that one was very easy. I have scouted the room with my spider familiar and we know what we are facing. The rogue and myself used stealth to get a surprise round and both gained initiative. The rogue did 3d6+3 and i 1d8+3, on second round the rogue hit the bugbear and killed him, on my turn i casted a Tashas Laugh on the second and the combat was over before even began.
The second fight we crossed paths with a group of scouts, was a Dragonborn Spy (MM349 with breath attack) and 4 scouts (MM349), again i scouted the room with my spider. The rogue failed his stealth check was notice but we are aout of sight of the room around a corner. The paladin moved to close the corridor (still of sight), the dragonborn moved to him and managed to hit. The rogue attacked the dragonborn and also hited, my turn, i concentrated a shatter spell and prepared to release the spell behind the dragonborn at the end of the turn, the cleric also moved but missed the dragonborn, then all scouts moved to get view of the party, unaware of my spell. On the end of the turn i got lucky and rolled 21 damage, all scouts failed the save, i did 94 dmg in a single round. The next turn the party managed to kill the dragonborn.
And the third encounter was against another group of scouts, 6 scouts, 2 spy (no dragonborns this time). Again i scouted ahead with my spider and this time we managed to get surprise, included the paladin. This fight was a lot more hard, i casted my last shatter and one burning hands and we won without any downed character. The paladin and the cleric stoped the enemys using dodge and sanctuary, myself and the rogue attacked from distance.
That was a regular day of combats for that group, at the end:
1o Encounter
Paladin Dmg 5/ Cleric Dmg 0/ Rogue Dmg 26/ Wizard Dmg 6
2o Encounter
Paladin Dmg 15/ Cleric Dmg 0/ Rogue Dmg 10/ Wizard Dmg 94
3o Encounter
Paladin Dmg 23/ Cleric Dmg 3/ Rogue Dmg 42/ Wizard Dmg 82
I always calculate info from the games i play like damage per character, and several other things to help me analyse the game.
As can be seen, with a wizard i managed to be top DPR in two of three encounters and the one that i was not i completely disabled the only enemy alive.
In no way im saying that a wizard HAS to be a DPR character, or that this is the best strategy, but what im saying is that IF he wants to be a DPR character he can be, after all the best status a controler can apply to monsters are DEAD.