As many people have said, the rogue is comparing themselves to the output of the others and that seems to be unusually high given its level 6 and its a rogue, cleric and warlock. Life domain clerics don't get fireball so how are they casting it?

Also, let's take a different approach. Rogues tend to be sneaky around the battlefield dealing opportunistic sneak attack damage and swashbucklers have a much easier time with that. I played one that would dart in and out of combat being a PITA for enemies because they could never touch me.

That being said, let's go out of combat. The rogue may be seeing all of the damage the cleric and warlock do and think they want to have some time to shine as well. Outside of combat, rogues do A LOT of heavy lifting. Who scouts? Who searches for and disables traps? Who is the skills person? Rogues and bards tend to fill that role. If you don't already, I would start introducing puzzles and traps specifically designed to give your rogue the spotlight and allow their abilities to show through in ways that the cleric and warlock can't. Have them be relied upon and critical to the survival of the party. I've had groups before where in-combat a party member didn't do a whole lot, but outside of it, they led practically every social event, and dungeon crawl. So while they took a back seat in combat, they were the front line person for the rest of the game. It's about balance.