Mono-white can break parity card and/or mana wise in a variety of ways but unfortunately its commanders are too trash to make it right to play generally.
You can build a pretty good token deck, a decent enchantment deck, a decent artifact deck, etc. But they're all worse than other colors because 1) the other colors offer something, 2) the other colors have commanders that are better.
Generally speaking it's true of all mono colors that they are worse than dual color pairs because of lack of a diversity of powerful cards. This is not true of 2 colors vs. 3, where playing 2 colors allows for a more consistent manabase and more utility lands, and the ability to play more demanding colored mana costs more consistently, etc.
It's true that a mono color manabase offers some advantages vs. 2, specifically with cards like Nykthos or Cabal Coffers and more utility lands, but this generally pales in comparison to the lack of card pool. Compare the power advantages of having access to green enchantresses and power cards (eternal witness, genesis wave, etc.) for an enchantress deck and it's easy to see this.
So all things considered the primary reason to play mono color is the commander. And mono white commanders are trash. They're simply awful in comparison to every other color.
The other four colors all have commanders who are literally competitive. Teferi, Arcum, JVP, Baral, Sidisi, Godo, Yisan, etc. White's best competitive commander is probably Teshar I guess? I honestly don't even know. they're all such miserable garbage.
Then if you move down the tiers to just 'very powerful' all four colors have those too (at least green, red and blue, not sure about black). White has a few decent ones too but literally nothing like Azusa or Talrand or Krenko.
You can build a pretty good token deck, a decent enchantment deck, a decent artifact deck, etc. But they're all worse than other colors because 1) the other colors offer something, 2) the other colors have commanders that are better.
Generally speaking it's true of all mono colors that they are worse than dual color pairs because of lack of a diversity of powerful cards. This is not true of 2 colors vs. 3, where playing 2 colors allows for a more consistent manabase and more utility lands, and the ability to play more demanding colored mana costs more consistently, etc.
It's true that a mono color manabase offers some advantages vs. 2, specifically with cards like Nykthos or Cabal Coffers and more utility lands, but this generally pales in comparison to the lack of card pool. Compare the power advantages of having access to green enchantresses and power cards (eternal witness, genesis wave, etc.) for an enchantress deck and it's easy to see this.
So all things considered the primary reason to play mono color is the commander. And mono white commanders are trash. They're simply awful in comparison to every other color.
The other four colors all have commanders who are literally competitive. Teferi, Arcum, JVP, Baral, Sidisi, Godo, Yisan, etc. White's best competitive commander is probably Teshar I guess? I honestly don't even know. they're all such miserable garbage.
Then if you move down the tiers to just 'very powerful' all four colors have those too (at least green, red and blue, not sure about black). White has a few decent ones too but literally nothing like Azusa or Talrand or Krenko.
UW Ephara Hatebears [Primer], GB Gitrog Lands, BRU Inalla Combo-Control, URG Maelstrom Wanderer Landfall
UW Ephara Hatebears [Primer], GB Gitrog Lands, BRU Inalla Combo-Control, URG Maelstrom Wanderer Landfall