My interpretation of your request boils down to "what's a good co-op roguelike" where the grinding is the replaying.

So, depending on how many players you need it to support and preferred genres, you might check out games like

• Risk of Rain 2
• Enter the Gungeon
• Children of Morta
• Vampire Survivors
• Streets of Rogue
• Gunfire Reborn
• Barony

There's also a game called Jumpship that i'm keeping an eye on the development of that's supposed to be hitting early access in the coming months.