The problem is that ENT itself gave mixed messages about Vulcan's location. The first season or two treated it as a fairly distant system, but then "Home" in season 4 locked it down as 16 light-years away -- the distance to 40 Eridani, the star that has generally been accepted as Vulcan's sun since James Blish first proposed it in his "Tomorrow is Yesterday" adaptation.
Although, come to think of it, Star Charts
was made when ENT was only a year old, so it went with 40 Eri out of tradition.
It also made a mistake by putting Axanar and some other first-season systems as close to Earth as it did. Mandel erroneously thought that NX-01 went back to Earth after "Broken Bow," when in fact it just kept on going from Qo'noS. So the systems visited in the early episodes should've been much farther away. Although then you run into the problem with the location of Vulcan space and places like P'Jem.