Gilmore was an established coach with a good track record. I think he was in a no win situation with Vangorder first and then when Elko came in and wanted to bring his LB coach with him, they needed to make room for Elston leaving Gilmore odd man out. In terms of straight up DL coaching, I would give the nod to Gilmore over Elston too but in the grand scheme of things, Elston had to be retained to salvage recruiting. Elston has also done a really good job as a recruiting coordinator and that is not something I could see Gilmore taking over without any experience in that role.
Booker though never really impressed me. I think he got elevated too quick and perhaps a step back will do his career some good. Still a very young coach with room to grow.