You see I think this is a point everyone in this thread (petty arguments aside) can agree on. All managers inherit teams, good, bad somewhere in between. Even the best of them fail for a while sooner or later. Martinez did a fantastic job with the squad he inherited and signed Lukaku (still our best player). Things went downhill fast but I think it's unrealistic for anyone to say that was due solely to Martinez's deficiencies - luck/players play their part.Also I mention Leicester because Ranieri is another manager who gained massively from what went before. He's now gone back to the form he showed as a manager in his previous jobs, including what happened at Greece. He to will be out of a job soon.
I have zero ill will for Martinez. He tried his best and did some great things. He also lost his job (think about that in real life terms) when things didn't work out.
Notwithstanding all of the above, I'm glad we have Koeman and I think he deserves respect and support from all of us (as Kendall, Royle, Moyes,Martinez etc etc did when they sent out blue boys in to battle).
COYB