Where you hire a bunch of assistants you trust and just delegate a lot of heavy lifting to them which is fine if you have people in place that know what the heck they're doing. In the case of Tuiaki, he had been coaching different positions but had never been a coordinator before. I remember in Kalani's first year, he was asked repeatedly if he was going to play any part in helping out with the defense. His response was always a defiant, "He (Tuiaki) knows what he's doing!" Tuiaki, to his credit has had his moments as DC but like a lot of inexperienced DCs, he struggles when offenses adjust to schemes. I think this season it got to a point where Kalani was like, "I love the guy, but he's gonna get me fired if I don't do something with the defense."
I actually don't have a problem with Tuiaki being on the staff but maybe DC is too much for him or he might benefit from a co-DC to help him out.