I think the real trend with RBs not being taken in the 1st is based on a common formula held strong by the NFL in general; only 3 down full tool RBs get 1st Round grades.
Run between the tackles?
Speed to the edge?
Run after contact?
20+ yard runs?
Pass catcher?
Pass protection?
There has not been a lot of 3 down RB1's come out over the last decade. These aren't the days of Priest Holmes, E James, M Faulk, L Tomlinson, E Smith, B Sanders, H Walker, etc, etc
Also, the offensive game has changed. While GMs are looking for those RBs that can plug into RPO and shotgun offenses, they will still salivate when they find the guy who can do it all. For the most part, they've allowed the supply of RB1s dictate how they draft and plan offensively. So many offenses can use RBBC and find interchangeable parts.
Why base on offense around a model of a rare RB1, that can stay healthy for more than 5 years and won't want a Top 3 salary on your team? Who are you going to replace him with when he misses a game or gets severely injured?
It's much easier to find a couple of cheap RBs who can collectively give you the same production without the price tag and can be replaced without much effort.
I like Harris for the Tua connection. I'm all about adding weapons for Tua and building around him. But if we don't draft RB @ 18, it's not the end of the world.
Let's face it, we won by "finding" RBs last year. It would be nice to have an Elite RB, but Flo obviously doesn't need one to win.