Should Rashford under normal conditions start on LW or even RW? Yes, he should. Flick knows that too.It was a shit decision by Flick not to start him today. He's not perfect and has his brainfart moments, but a much better winger than Fermin, let alone Bardghji.
Flick also knows that he needs the money for other positions to strenghten though. And that's why he is giving Fermin game time on that left wing. He is thinking mid-term, not short-term. When everybody is healthy Fermin will find it hard to play the big games.
Now is not only the time to win the championship. It is also the time to test things for Flick due to the comfortable situation in the table.