This is the world cup year means players give their best so we could see if he can improve this season. Same applies to Shaw/Maguire/Rashford/Sancho.
We played our best football with Martial-Bruno-Rashford-Pogba as front 4, so talent is still there.
That part is a myth. Players may be reluctant to a big move before World Cup, but they don't necessarily give their best for the club. Unless it's a big stake like CL games, the players are more risk averse. They would be more cautious about small injuries, rather pushing to play every games by playing with small injuries.
Before the last World Cup, all Shaw and Martial had a meh season in term of effort. Pogba was in and out of the team with injuries and other issues.
Martial best football and most productive period came after the restart.
Intensity was at lower level because training regime for all team was negatively affected. Individual talent especially dribbling gained an edge during this period.Team relies on high intensity and teamwork like Man City and Liverpool came back worse after the restart. Someone like Kane who was injured before the COVID break, then not be able to access to normal training, was unfit after the restart.
Low intensity football from both teams suits Martial. It gave him an edge that time.
Then there is this reality that France have a great pool of attackers for selection. Martial is now way down the list with Benzema coming back. For a more winger type, Coman, Dembele, Diaby are better options. Supporting forwards they now have Griezmann, NKunku. Giroud and Ben Yedder back up and alternative to Benzema for CF position. Mbappe is Mbappe. He's the ace in that team. Be it 2 or 3 upfront, he would get his name in. By now, France pretty established the core players as well as the B list. So for Martial to get back in there in in few month time, it would require he to somehow play in Ballon d'Or form as well as injuries to some of the core players. With ETH coming in as new manager, Martial is fighting the uphill battle to earn game time to begin with. So effort alone wouldn't matter much. That playing in this World Cup ambition is highly likely way way out of his hand now.