Keep in mind my knowledge almost entirely comes out of DCS, a combat flight simulator game.

> maybe that's legacy now

No as far as I'm aware it continues to be a thing, to assist in keeping on glidepath.

The lineup system is for aligning to center line (horizontally relative to carrier's deck) from a distance. I did find it odd that there is barely any mention of it outside some internet forums, the closest to an authoritative source I found was this https://www.cnatra.navy.mil/local/docs/pat-pubs/P-816.pdf (see Page 24)