New Monk is Stomping my Monsters and other players are feeling useless

So like the title says I am DMing Vecna eve of ruin and my monk is literally doing 60 damage a round with nick and flurry of blows. He is melting bosses even with multiple encounters and my other players feel like they do not contribute what do I do?

Edit: The party is a warlock pally a fighter/cleric multi class a dance bard and a halfling evocation wizard they level 13 right now. Another problem with this combination is that they all get absurd initiative roles from the dance bard ability they all have someway to see inside magical darkness because they designed the party around the monk shadow abilities. Not only are my monsters not being able to see they are always going last. And specifically the paladin feels like he isn’t contributing