In "The Next Phase" it's suggested Geordi's engineering expertise is what interested Picard in him in the first place so Geordi is likely brought onto the ship with the intention of him being Chief Engineer someday. Since Geordi was then only a Lieutenant J.G. he had to wait for a promotion to get the position and he hadn't put enough time in at the lower rank. Meanwhile the Enterprise served as a "training ship" for other engineers to be assigned to future Galaxy-Class ships or ships with the new systems the Enterprise had. (Hence the rotating series of engineers we see in the first season.) Geordi would spend a year as the chief helmsman at Lieutenant J.G. while ALSO learning about the ship's new systems behind the scenes, meanwhile the ship would train aspiring engineers going to future assignments. After a year Geordi would be open for the promotion to full Lieutenant, get it, and then be given the Chief Engineer role on a "fast-track" to Lieutenant Commander. (Which he would get by the third season.)
This really makes a lot of sense and ties in the rotating Chief Engineers nicely.