First off, we got Marshawn Lynch for a 4th round pick. We didn't spend a day one pick on him. We got immense value out of that trade. The Seahawks would have been stupid not to take that trade.
Secondly, not drafting a RB day one =/= not caring about the running game. The RB position is a short lived position and it's also the easiest of the skill positions to plug and play. We already have a great player in K9, what we need now is a role player to fill in the gaps. With Dallas as our third down back, K9 as our bellcow all we need is someone for those tough yards. That doesn't call for a first day pick.
First off, there is no doubt in anybody's mind that Lynch, at that point of his young career, is DEFINITELY the value of an early day one pick. Seattle gave up two firsts for Jamaal Adams. Are you trying to convince me that, in hindsight, knowing what they now know about Lynch, they wouldn't give up the equivalent for him? Knowing what we know now, if they had the equivalent draft capital in their back pocket, and had to make a choice between Lynch or Adams, who do you think they would choose?
Further, there is no such thing as a "short lived" position. There is only the rookie deal or veteran minimum, and that is what levels the playing field for ALL positions. Players are offered to renew (or not) dependent upon their productivity and demonstrated potential of their first four years with a third renewal being quite rare regardless of position except quarterback. THAT is what defines "short lived" because extending into the veteran minimum salary is what defines a given player's tenure. Hence, if a running back typically only lasts eight years, then it is consummate with the salary structure of one renewal. Relatively speaking, that isn't much different than any other position.
Additionally, the league is chock full of "Short lived" positions. Look at what the Rams assembled for their brief Super Bowl window and then look at how they are currently dismantling their expensive roster. The last thing they cared about is the life span of any given player's career. They are only looking for the short-term talent burst to put them over the top. What follows is a cap induced fire sale because no team can escape the inflated salary demands of a roster full of ring bearers. A lot of "short lived" turnover happening there.
Further, because you don't spend #5 on a running back, the resultant "trade down" parlay is defined as quantitatively more than just a running back. It is in addition to another valuable position player chosen on day one as well. In fact, for that #5 pick, Seattle could get day one picks of both a nose tackle and a running back with the running back likely being the best back in the draft and the nose tackle probably being a first-year starter.