The problem with your analysis is that you're expecting us to get multiple starters from this draft class from the get-go. That's not realistic.
What is realistic is expecting your first rounder to be a starter immediately, and your 2nd and 3rd round guys to be contributors - even if they aren't starters.
Just because we signed JAG's to fill needs in the off-season doesn't mean we won't or shouldn't address those in the draft. If a highly graded Guard or Safety on our draft board is available at #14 or #45, I doubt we pass on them just because we addressed those positions in the off-season. Guys like Pool, Livings, and Bernadeau are temporary fixes that were signed to give us flexibility on draft day, not as permanent solutions. They're security blankets so we're not forced to reach.
Harrison Smith would compete for a starting job this year. Brodney Pool is by no stretch of the imagination a permanent solution at safety. He's been a JAG in his career thus far and has had problems staying healthy. If Smith doesn't crack the opening day line-up, he'd still see a lot of action IMO and be used a lot like Church last season. Not to mention the games where Pool will be hurt and he would step in and start.
Irvin not having protypical size at this moment isn't an issue, since he would likely only be used in pass rushing situations his first season.
Solid Draft OP. You address three needs with the first 3 picks, and they'd all be able to contribute THIS year. I'd like to see us go DL with one of the first three picks, but this team has so many holes that you can't address them all with one draft. All you can hope for is to get as many talented guys as you can.