Brawl is supposed to be limited to cards available in standard. This is directly from wizards' page announcing brawl:
Each player's deck is exactly 60 cards. Other than basic lands, no card may appear in a deck more than once. Each card must be legal in the Standard format; cards banned in the Standard format can't be played in the Brawl variant.
Cards banned in the standard format can't be played in the Brawl variant.
...
And yet Uro, even after being banned in EVERY format, remains available in MTG Arena Brawl.

Uro is in nearly every deck containing simic colors. Fires of Invention is in nearly all Kenrith decks.

Please follow your own rules and get ALL of the cards that are banned in standard out of Brawl.

Edit: I realize that the rules have been amended since Brawl was released and has it has its own particular ban list. I do appreciate the cards listed there (Drannith Magistrate, among others) which do harm to the format.

That said, there are reasons that certain cards get removed from standard. Keeping the cards which have received bans simply because the format is singleton does not remove the play patterns that got them banned.

Cat/Oven, Fires of Invention, or Uro (especially as the commander) do harm to the game.