Is this the way you train all your other bodyparts? Then why would you train the abs that way. It's a muscle just the same. You need to apply basic principles of hypertrophy to the abs as well.
Heavy resistance, low-ish reps (8-10), and progression over time. So choose weighted crunches where you can add weight. An ideal exercise is crunch over a swiss ball for full range of motion and stretch, and hold a weight over your head for added resistance.
As you build up the abdominal muscle, it will push through those "tendonous structures" that cause the separation. Building bigger peaks makes for deeper valleys.
That's how you'll maximize your genetic potential.