...Rose needs to be replaced.

Look at how his coaching staff has changed over the years and how the success of the program has changed along with it. Ultimately I think the speed of the leader determines the rate of the pack, but in the past Rose has had really good assistant coaches on staff who made significant contributions to the direction of the team. Early in his tenure he had assistant coaches who went on to bigger and better opportunities. Dave Rice, Mark Pope and John Wardenburg both left BYU and eventually landed head coaching jobs. Walter Roese also moved on to bigger opportunities including a job working with a Big 10 team.

With Lacomb and Nashif, both guys have basically just hung around carrying clipboards, picking up towels, editing videos, etc until openings on the staff led to bigger and better things. When Roese left, Nashif got promoted and the same thing happened for Lacomb when Wardenburg left iirc.

It's nice to be loyal and have assistants loyal to you but I think there's value to having assistants who have traveled, built relationships and networks of friends and contacts in a variety of areas and can bring new ideas that help expand the gene pool of thought at BYU. I get that it's comfortable to stay with the same guys and easier (you don't have to do a bunch of interviewing and vetting of candidates or go through the hassle of getting to know and building chemistry with a new assistant coach) but when all that the assistant coach knows or has experienced are all the same things you already know and have experienced, it seems you are closing the loop on growth and progress (and putting yourself at risk of having a bunch of "yes men" surrounding you).

If you look at the heyday of BYU football under Lavell, it was when he had a steady influx of new assistant coaches bringing in new ideas and then moving on to bigger and better things. When the program started to get stagnant it was when his coaching staff started planting deep roots and there was very little turnover. If you have good assistants, more often than not they will be sought out by other programs and you will lose them eventually. If you have assistants who don't bring a lot to the table, they will stick around as long as they can until the head coach gets let go.

I don't ever hear of other programs trying to lure Nashif or Lacomb away yet in recent years both Pope and Rice have been. I think that's a pretty glaring indicator right there of a problem on the coaching staff that needs some action.