To say taking a team from 6th to 11th (via 5th) being 1 of the worst managerial performances you've ever seen is hyperbole, especially when Moyes managed 7th to 18th during his own spell in charge, and 1st to 6th with united, and Ranieri is currently overseeing 1st to 16th. So once again, I would call that an overemphasis.
You also make the assessment that Martinez agreed that Moyes left us strong by using 8 of those players, to somehow prove my point wrong, when my point wasn't that he there wasn't a core of a decent team there, but that it was nearing the end of a cycle and would need replacing in the near future. I said as much in a few of my points, and that I believed he took the gamble on spending 2 years worth of budget on Lukaku to compliment what was already there, under the impression the spine of the team would make do in the meantime.
Unfortunately the same spine, and it was the same players as you rightly point out, let him down badly over the next 2 years, mixed with the younger players he introduced lacking in confidence.
As for Koeman replacing them all, again, I keep having to go over the same points, Koeman was brought in with an entirely different set of limitations to that which Martinez was managing under. A new billionaire owner, the ability to spend vast sums of money on established players and discard the older players who were no longer deemed good enough is a luxury he has knowing the weight of the financial muscle he has behind him. He is also able to call upon younger players that Martinez championed (Davies, Holgate).
We are never going to agree on this, so it seems pointless to continue. The frustrating thing is, I'm not trying to convince anyone Martinez was better than Koeman is or Moyes was. I'm just trying to say he doesn't deserve as much derision as he gets and there should be more reason applied to his time in charge. Rightly or wrongly, he helped shape where we are now.