I think he will come good too, but its imperative that we get to spend in line with the expectations that have built up, and he makes the team/squad his own. Then he can be judged fairly.
The squad has deteriorated to such a degree in my view that RK will only have limited gain in things like tactical reorganisation and whatever motivational techniques he can avail of.
In many ways it is the perfect storm which he has inherited. Rising expectations which are at a 25-year high coupled with the natural decline and aging of large parts of the squad, and the damage to good habits, consistency, and discipline inflicted by his predecessor.
Whomever succeeded Martinez would have faced the same uphill challenges. RK is certainly responsible and accountable from day one, that's what he is paid for. But he is certainly entitled to some slack also.
EDIT: It also strikes me, that whilst I was not a particular fan of
Moyes, he did to his credit shield us for a decade from the true costs of underinvestment and inept business management. Take Moshiri out of the equation (and you can do, as this squad at present has not benefitted from a big cash injection) and you just see the end-results of a generation of stagnation. Time has caught up with the present squad exacerbated by the lack of a steady hand (Martinez) and this is what Koeman has walked into.