Estrada has a K/9 above 8, BB/9 under 3, inducing more grounders/fewer liners/less fly balls, yet his HR/9 is up. SwStr% is up slightly, and his contact rate is down. I see the same things you are seeing in his starts. He's always going to be a bit prone to the HR, but he should settle down as a 3.50 ERA, 1.25 WHIP type of starter. Keep him.