I think you are delusional about what a good draft class is. If a team drafts 3 pro-bowlers, then that draft class is exceptional and maybe even a little lucky. If a team can get two legit starters every year, then they will turnover half of their starters (10 of 22) in a mere five seasons.
Sure McKinney was a first round draft pick, but he has started since day 1 (of signing) and has held down the left tackle spot. He still has more potential to grow into, but this pick has returned a lot of value to the Vikings. Better yet, if he was a free agent, what do you think teams would pay for him? Lets not forget what it costs to sign a player like (FA 2005 - Jonas Jennings – Bills).
Raonall Smith has been very hampered by injuries, but has shown that the reasons he was selected in the 2nd round are legit; the ability is there. Been a solid contributor on special teams and added valuable competition for both outside linebacker positions. Has even started a few games when needed and played well (not great).
Willie Offord was a 3rd round pick? What kind of value can a team find here? A guy to come in and play the nickle-spot for three years and be an adequate backup safety? Again, great return on the pick.
Brian Williams has been a solid starting cornerback for two years now. He is no way a shutdown corner, but more than serviceable for a fourth round pick. Lets not mention that has a restricted free agent, he would garner a 1st round pick. Obviously not worth that, but for a 2nd or 3rd round pick, I am sure another team would have bit. Again, great value from a 4th round pick.
Edward Ta'amu is no longer with the team, but played two years and showed that yes he had potential, just not enough. This is fairly common for a fifth round pick. Being able to make the roster is a worthy accomplishment; making it twice is noteworthy.
Nick Rogers, give it up man! He was a 6th round pick. These guys are unlikely to make the team in their first year, not to mention their third year.
Chad Beasley I know nothing about other than he was picked in the 7th round.
Maybe I am wrong, I am willing to acknowledge this. But you have to show me multiple teams that consistently drafts 2 or 3 starters every year, at which point, relativitely speaking I will acknowledge the Vikings have a poor track record in the draft.