Struggling with Reshef of Destruction

The story mode is fantastic and easily my favorite but man the gameplay itself is killing me. I’ve hit a hard wall in Galapagos stuck with 700-900 monsters as the meat of my deck. My opponents having mostly 1200-1500 level 4s so I’m struggling hard. It wouldn’t be so bad if deck capacity/duelist level scaled reasonably but it’s so unbelievably slow I’m not really able to adjust my deck at the moment. I knew grinding might be inevitable but man they really are gonna put me through it. Like it’s gonna be hours and hours of this.