How far into the game are you? Without context it's hard to answer, but judging from another thread you created, my guess is relatively early?
If you happened to get another rare/epic/etc that can do the job better than him, you could leave him on the bench/eat him. But your starter champ is typically far more powerful than anyone else you can get at that point in the game. It's almost always a good idea to start by getting your starter to 60, so that you can farm campaign. Even after you get other, better champs, it'll be a while until you can have a dedicated campaign farmer, so he'll likely still carry value.
I would take Galek to 60, followed by Tayrel as your defense down/attack down (also will be using him as your clan boss lead, as you build that team out, eventually). Galek will serve as your campaign farmer.
Then I would go Rector to 60. Those three will help you form a nice core to your dungeon grind, early. While Gorlos has a shorter cooldown on his defense down than Tayrel when booked, Tayrel (and Rector) will offer up a lot more utility and be better investments long term.