Using Post-Processing through EffectComposer causes jagged artifacts on model [Browser: Safari]

The standard antialiasing of the WebGLRenderer({ antialias: true }) is MSAA, which is not used with the effectComposer. You could try to use FXAA, but the result will be different/worse.
If you want to use PP and MSAA, you have to go for the multisampled rendertarget (This is only supported with WebGL2)

Using SSAARenderPass you’ll get a even better AA than with MSAA, but it costs performance

See this discussion