No pick is a guarantee, just ask the Jets (and you can look at a lot of 1st rounders picked before ours who've busted).
I'm not trying to defend CB, and I'll give you Hooker. Even though at the time everyone thought it was a steal, but injuries did him in.
So what if Buck was a 49ers pick, we got him cheaper than they did as far as draft capital.
Bottom line, "First round grade" is subjective and hindsight is... I'll still take CB's draft success over most GMs.