this is the bit I'm struggling with
"...(T)hat I`ve said is that there is little point in sacking him(since there is absolutely no guarantee that any incoming coach will fare any better)"
There is no guarantee in anything if we are going to that degree.
No team would ever change coach on that basis (that's what I mean by changing the level of the argument from a Macca specific one to a far fetched claim that no coach could be guaranteed to do any better).
I think its a fair call to say that other coach (unnamed, perhaps unavailable coach) could potentially do better.
Your reasons for wanting to stick with Macca or not having yet made up your mind or not wanting to judge are all, of course, perfectly reasonable. But to say that he shouldn't be replaced as no coach could be guaranteed to do better is a false premise and an unsound argument.
Having said all that I'm prob being uncharitable in my reading of your post, but I just can't resist illogical claims. All the best, Si