I've read all 5 pages of this so far and its a really good read to see this discussion by knowledgable Saints fans about your former coaches.
As an outsider (Warrington fan) I am surprised to see some people saying they rated Millward above Anderson, IMO Millward was massively overrated and had the good fortune to enjoy 5 years of about a 10 year period when Saints had the best squad in the game. I think if DA had taken over Saints after Hanley then Saints would have been like Man United, won nearly every season, instead of only winning 3 SL titles in that time. It still shocks me that Bradford won 3 titles in that time because you look at their squad against Saints and they were good but in every dimension they were a slightly lesser version of Saints: Lowes/Cunningham; Withers/Wellens; Forshaw/Scully; Deacon/Long etc. I thought Millward built a reputation on controversy and big ego and he rode off the bandwagon of a great team which enabled him to pick up trophies, but he was hopelessly exposed at Wigan as not up to the job. Anderson IMO is the best coach in SL history with Tony Smith close behind.
I would have jumped at the chance to get DA as Warrington coach but I would never have wanted Millward, I doubt Millward could have achieved any more than Cullen, whereas I think DA could have done what Tony Smith has.
As for Potter he took over a team at an awkward time, where there are a lot of great players who have won a lot of trophies, slightly past their best, and its difficult as a new coach who hasn't won the trophies with those players, to manage the transition, look at Liverpool under Souness or Leeds under McDermott. In those circumstances I thought Potter, and now Royce, have done the job well because Saints have been within touching distance of trophies and still are. But neither Potter nor Royce are in the league of MacGuire, Smith or Anderson.