Don't forget about the business side of the positional value. You have to gain money on your rookies to be able to pay your veterans. The guy who we will pick at 1/3, will earn cca 5 millions per year during his rookie contract. If he is an ILB, his contract will immediately make him the 7th highest paid inside linebacker in the league. The seventh. You practically loose him as a rookie, because he'll earn more than the majority of veteran linebackers. If he won't become a Luke Kueckly, just an very good to above average ILB, you will actually LOOSE money on his rookie contract. The has to become a Kuechly in order for you to gain money on his rookie contract, and even then, it wont be more than 4 to 7 millions per year.
On the other hand, if you draft a pass rusher, his 5 millions per year salary won't get him inside the top40 of the positional salary list. If he'll just become an average player, he'll still demand 8-10 mills as veteran, so you will still gain 3-5 mills on him. If he becomes an above average player, your financial gain go up to 8-10-12 milions. And if he'll become a Mack, Von Miller, Watt, you'll gain 15+ mills per year.
I'm talking about the top5. Maybe top10. Rookies salaries drop quickly by draft position. So, beginning with the second half of the first round, and down, the financial impact - and the difference between a first round and 3rd round pick - is irrelevant. You won't gain/loose relevant money if you pick your RB in the end of the first round or in the 3rd.
So either trade back, and pick whoever is the best, or if we pick at 1/3 we have to pick for a finantially important position. If we don't, we will pay the price later by not being able to retain / hire a veteran for a different position.