It's a fair cop. The pyjama jacket was never developed with bedtime in mind. It is, rather a mid-layer: an almost-a-jacket, unlined and unstructured, which serves as a loose and laidback jacket in warm weather, and yet can be something squished comfortably between a shirt and coat at cooler times.
Collars like this you don't often see, unless you spend lots of time at museums dedicated to mid-century rail uniforms. It's what's known as a one-piece collar (though in point of fact, this one is made in two pieces) which drops low at the front, and fans out neatly thanks to the underside having a small inbuilt notch.
It has a two-piece semi-raglan sleeve: a sleeve truly of a bygone era, superseded by the full raglan sleeve. There's lots to like about this anatomical anachronism. It has a natural roundness, which gives the pyjama a soft shape that fits in with the rest of its sandman-approved styling.