This is an excellent point and you will not get a meaningful response from those who complaint that it takes rookies too long to see the field with the Steelers. First, talented rookies with weak starters in front of them start early - guys like Hampton, Kendrell Bell, etc. Cortez Allen contributed as a rookie and played more this year because he showed that he was ready. Lewis didn't play early because he was not ready to play in the NFL. He had the meltdown in the preseason game last (or maybe two years ago) and was not ready.
Giving rookies a year or two to learn and be slowly worked into games is a luxury - not a problem that needs to be solved.
Moreover, look around the NFL. The rookies that start typically do so on bad teams. There are two reasons for this - first, bad teams pick higher in the draft and are able to select better players. Second, bad teams are bad for a reason - usually because their starters stink. Finally, if you're not playing for anything, you can allow a rookie to make mistakes.
A final point - most rookies are not stars. Leaguewide, a few guys step in and contribute as rookies, but they are the exception, not the rule. Many players, even those in - gasp - a 4-3 defense, take time to adjust to the NFL and take time before they contribute at a high level.
Can you really afford the "luxury" when you constantly create a situation like we have with Keenan Lewis where you get a one full season sample size and then have to sign him to his second contract for big money? A rookie doesn't have to be a starter, but they should be able to get a lot more in game experience so you can both develop and evaluate him.
Playing Fantasy Football does not qualify you to be the in the front office or on the coaching staff of the Pittsburgh Steelers. They are professionals and you are not!