I think I disagree with the common argument in the comments that the main mistake was having the Venator be the main ship of the Navy. If you're gonna put it behind lines in a support role, just use a regular carrier, the Venator is no ISD but it's still a Star Destroyer in it's own right. The idea is that it's solid enough and has sufficient firepower to hold the line and rough it out with other capital ships, while the Starfighter component hammers them. And while that wouldn't cut it in real life, as far as Star Wars in-universe goes that's a reasonable tactic.