The answer to the question, "Was Bill a great head coach?" depends simply on what year you are talking about. For a while he was, then he wasn't. This is a classic case in which a simple clarification of the question makes the answer - answers - clear.
As for the Tom-vs-Bill controversy - "Which guy is really responsible for the dynasty?" - this is akin to asking, "Which is more essential if you want to make salt, sodium or chlorine?" Both are ill-formed questions to which any answer is incomplete, erroneous. To return to our evaluation of Bill, the manner is which he was able to coach was dependent on Tom's remarkable skills and character. Because he was a great coach - for a time - Bill took advantage of Tom's skills and approach to the game. That is precisely what a wise coach would do. Then he stopped doing so, seemingly motivated more by an increasingly childish, even pathological need to retain his standing as the alpha in the relationship than by any commitment to "what is best for the team." He brought the same irresponsibly emotional and personal and ultimately petty motivation to the several bonehead moves with which we are all too familiar - from his ill-use of Mac, to his delusion that Tom was unnecessary to the manner in which he had such great success, to indulging in a Superbowl -losing snit with a DB who had dissed his fat Pal (or some such transgression), to assuming that his ass-kissing acolytes were so brilliant that he could dispense with simple diligence in building a coaching staff, and so on.
I taught a philosophy class for 25 years. Most of the useful work in that discipline is the yield of the simple practice of defining your terms and clarifiying the questions to which you are seeking answers. If you don't do that work, every argument is mere posturing, and every discussion just becomes a pissing contest.
As for for the present state of affairs, it's just very sad and embarrassing. Because death is literally inconceivable, it tends to remain abstract for we human beings, which a little paradoxically makes its inevitability comparatively painless to acknowledge because its reality is unavailable to thought. Not so with with the decline which precedes it with equal inevitability. A man's decline is protracted, generally ugly in various manners, painful, and plain for all to see. It is discouraging and relentless. How much worse it must be for a man with Bill's celebrity, where that decline becomes fodder for essentially idle banter and such pontification as this post might be. For celebrities, the private becomes public. How painful that must be.