Why does everyone fixate on the back injury when it was Costa's ankle that cost him so much time last season? He missed, what, 3 games because of his back, then came back and dislocated his ankle a week and half later.
And Costa was never as bad as some believed, and looked to have improved a good amount last offseason. I have questions about his health, and, like any position, if you can improve the talent there, you should do it, but he's a capable starter in this league, very likely our expected OC for the next few years, and probably not somebody they team's planning on replacing early in the upcoming draft.
And if they were, it wouldn't be with a career OG who learned to take a few snaps to try to up his draft stock. It'd be with Bernadeau, or with a 3rd round career college OC.