If Campbell can be more like Cam Talbot (aside from his one really down year in Edmonton) but 5 years younger, that's fine. No one is asking him to be Vasilevsky, even though he had an identical save percentage to Vasilevsky in that Bolts-Leafs series (had really strong playoff numbers the year before too).
Smith's numbers were buoyed by a hot stretch right towards the end of the year, but he had a lot of shit sub .900 games prior to that too. He went on a 8 game heater to close out the season, that really buoyed his save percentage.
Koskinen was a non-starter as he just doesn't have the upper tier game that even Campbell has, Smith is turning 41 years old and injured so obviously that wouldn't work, Kuemper was the other main option but having to "retrain your eye to see properly" was a scary proposition with him.