Stars remain pinpoint when looked at even with a small magnification telescope
Their brightness also varies considerably more than is allowed by dynamic range of an 8-bit display. The only way to make brighter stars sufficently distinguishable from significantly dimmer, but still visible, stars, within the constraints of an SDR display, is to make the brighter stars cover more pixels.
The Exec with 2.6x scope should not bloat any star, but i guess is not easy to reproduce that, certainly with no performance penalty costs.
No, you're right, it shouldn't.
It also shouldn't be terribly hard to tile the skybox, render it at a sufficiently huge resolution and down sample it as necessary, even on the fly. However, the skybox is unique to each system, and has to be generated on the fly during a hyperspace jump, and that is where the bottleneck is. Everything that can be seen from that system via the galaxy map needs to be distilled down to a 2D texture in a couple of seconds of render time. They should probably be doing this in the background and caching skybox images, but that would take a lot of RAM and exacerbate already sketchy performance.