I have a 60 gallon tank with a ecosystem. It is an established tank of 1 1/2 yrs. I have never purchased a protein skimmer and the tank is doing fine.
If your tank is doing fine, I wouldn't change a thing. Protein skimmers remove disolved organic compounds from the water before they can break down and create ammonia-nitrite-nitrate. It is an ongoing export system.
Many Eco-Systems come with protein skimmers now. Years ago they were advertised as perfect as they were and that no skimmer was required. Eco-Systems feels very strongly about their Miracle Mud substrate.