Of course you must heed mistakes of the past, but similarly sometimes you don't change for the sake of it, there is a lot to be said in teams and brand values to continue development and progression, not bring in a new figure head who changes a lot..... Few can argue we have progressed in four years.
I think the distinction with AH's experience is that unlike the others mentioned when they got the top job - AH DOES have experience of bad times, relegations, struggles and has been around those things, particularly thinking of Steady, he had not. so when it came it was new to him and hard to handle.
I would also suggest respectfully of AH's career compared to Steady's that he was not a natural athlete and it did not come as easy to him as it did to GS - hence why GS struggled with the training mentality and instilling the discipline of looking after yourself for players, where AH I would suggest had to work a lot harder. (Note here, I would love to have been as average as AH, I have no discernable sporting talent and anyone who ever saw me with a ball or boots will tell you that)
I am not wedded to any plan to speak of, but each new coach has to get a shot sometime.