He won't do the Steelers any good and vice versa. Misery meet misery.
Two reasons he might do them a world of good if he didn't totally fall off between last year and this one.
First reason is that If they put him in the slot he's enough of a tactician to win quickly and Rodgers's aDOT is minuscule. His time to throw is or was among the quickest in the league in Pittsburgh, and they just lost their left tackle, so these are quick hitters. It is going to require the footwork and body positioning that Thielen has had his whole career.
Second reason is that on intermediate routes, Rodgers just complained about a lack of attention to routes called and route detail. Thielen will come in and get it, if not by the first game, then the second one. He's cooked compared to Nailor and Addison, who both run way under 4.5. Thielen was never going to beat those guys out, but he will run precise and deceptive patterns that win at the top of the route so Rodgers can make anticipatory timing throws.
Will this be a success? Watch for how quickly he picks things up and his athleticism. You'll know within two games.