It definitely has been. He's scored a couple of fantastic goals which - in isolation - give the impression of a good run of form. But his form hasn't been great at all. For example, both of his wonder goals came in games where his overall performance was average to poor. In a way, Lingard's the opposite. His hot streak of scoring has dried up but his overall performances have been just as good as, if not better than, what we saw when he was scoring in every game.
Martial's a weird one. Sometimes he looks incapable of the most basic of skills. His short and medium range passing along the ground is generally pretty diabolical, for example. Can anyone ever remember him playing a penetrative through ball? Because in every single game he plays there's usually at least one seemingly straightforward pass from him that almost takes your breath away with its astonishing inaccuracy. Then we have his (lack of) movement. Lingard, Rashford and Lukaku (for all their flaws) are constantly giving an option to our more progressive passers, with clever runs in behind the opposition defence. Martial more or less never gives this sort of option. So you're left with someone who has exceptional dribbling skills (yet seems to have got more and more one-dimensional: constantly cutting inside onto his right foot) and an ability to occasionally curl a screamer into the top corner. Which are nice qualities to have in our team but arguably not at the expense of playing someone who does so many other important things so poorly.