You're right, he's not an all-star. But Breeland is easily the best zone corner available. Good enough to command a contract of 3/24 when he was thought to be healthy. And he was ranked as a top-40 free agent on every reputable top-100 free agent list. NFL.com, PFF and ESPN.com.
So, he may be average, or slightly above average, but no one here is sure that we have any one better. Someone from our collection of unknowns may wind up being that, but no one knows for sure. We're all guessing. I'd be very happy to have him signed, especially since Wilson apparently didn't play much this spring due to some unknown minor injury.
I don't see a downside to signing Breeland with a decent chance for a good upside. You don't often get a chance to sign someone of his ability to a bargain contract. I'd take it.
As time goes by and the more time he misses, we can forget just how good our QB can be when healthy. If he really is better than he's ever been, I'm definitely excited to see what he can do. Even if he's just "only" as good as he was before surgery I'm still pretty intrigued. Here's a nice reminder.
I'm glad they are doing their due diligence with him. I watched him a bit last season and I thought he was worth about a 5th-6th round pick without knowing he had issues with coachability(I heard about those from Matt Miller on his Stick to Football podcast when he declared for the supplemental draft). Now I'm wary giving up even a 5th... but that's why Ballard and his staff are paid millions - to do their research and see if there is fire where the smoke is.