I think you're being ridiculously harsh, he often has to step out from the back because the midfield can't be arsed doing any defending. He has to step out, he was excellent in the first half last night, he struggled in the second but that's more because of how exposed our defence was.
He doesn't have to step out so often & he certainly doesn't have to step out & sit on the floor. That is his own doing, entirely.
Top defenders stay on their feet whenever possible, he goes to ground all the time, thus taking himself out of the game & has even been found out diving. That is not a 'top defender' by any stretch of the imagination & we need 'top defenders' at cb. He lets players drift in behind him & has been out muscled even by quite small attackers, skinned for pace & strength by one of Watford's cfs last weekend for example, nutmegged by another, he looks great winning headers from goalkicks & attacking corners but rarely wins anything from a dangerous cross or corner in our box, passes it on.
Right now he is not as good as many of the run of the mill cbs in the top half of the table. Some journeyman like Jagielka or Collocini would be an improvement on him at this time. His performances are masked by the fact that the people next to him are often the current worst central defenders in the Premier League & the unit is totally disorganised.
But he is agressive & a decent tackler, not bad on the ball, ok in the air when not heavilly challenged, so he has the basics to work on & I'm hopeful he will come good. It's not easy being a cb in this godawful defence & he was always going to struggle coming straight to the Prem from Spain & not being very big, or quick.
Spain is a very clever technical league full of diving wusses, where he is a 'tough guy'. The Prem is a dark alley full of people with baseball bats who don't give a fuck about his tattoos.
He is unfortunate to be working for Pellegrini. In an organised defence, with some guidence, he might have settled a lot quicker. Pellegrini has no idea & is being found out by the other managers.
But there is still hope for Otamendi to realise his potential, especially if VK comes back one day. His performances from now on may be key to our season. Demichelis was almost as bad in the first half of his first season & came good, so hopefully Otto can. We need him.