A single round of noise ("code capacity") is a good model for a perfect sender transmitting to a perfect receiver over a noisy quantum channel. It's a bad model for a quantum computer built of imperfect parts trying to preserve its quantum information despite those imperfections ("circuit noise"). Circuit noise is the more important problem, because it's what what determines if you can even make a good quantum computer in the first place.
Note that circuit noise is distinct from doing multiple rounds of correction where it's assumed that measuring a stabilizer is an atomic operation ("phenom noise"). Phenom noise is a much better approximation of circuit noise than code capacity noise, but still falls short in several respects. It insufficiently penalizes large stabilizers, for example.