Very true but I agree with
@fps that post-lockdown Martial is really looking the part as the central-most prong of that attack, and his hattrick against Sheffield United epitomises what you get from him as a central player; receiving two balls from wide which he puts away clinically and then dropping slightly deeper to profit from a nice give and go with Rashford, all done within the width of the 18 yard box. Don't get me wrong as you point out the goal he scores against Bournemouth comes from him drifting out to the left, but I think even in that game what strikes me is how fine a central striker Martial looks these days; for Greenwood's first goal (from the left as you say) Martial is the man in the centre, he puts the ball back across goal for the penalty after drifting to the far post for Shaw's cross and he's central and alive in the box when Greenwood scores his fourth from the right.
He will surely be a player that likes to move laterally but my point is I love how his game has come on within the width of the 18 yard box, where before he was as times not involved for long stretches in games and looked constantly to be drifting wide just to get a kick of the ball. I've no doubt he's been aided by Greenwood's emergence as a fine inside forward, not to mention Bruno behind him, but I think he should also take credit for the improvements he's made as a more central striker.