I believe you're misreading it, actually. Steel is said to have the skills to control the computers to "help them get back". That's one thing. Then a second point is made that, if he remains outside, he can close the door they just opened if something is trying to come out from the gate. That part isn't stated to require any particular skill, and you probably just have to type the right command to do it.
But Doomsday and Zod didn"t come out from the gate because it was shut. How Doomsday came out is still a mystery, and if my memory serves me right, Zod escaped using Warworld technology. So Steel wouldn't have been useful.
Plus, it's probably more a "of all of us present here, you're the most likely to" than "you graduated in Phantom gates closing in college" kind of thing. It's an improvised plan, not a strategy.