My concern with him is his productivity. He doesn't score enough but even when he was out wide, he didn't cross the ball. Look at rashford; similar age, similar number of games played, stuck out wide a fair bit. Rashford has more goals and assists and put far more crosses into the box.
Nobody doubts calvert lewin's effort or attitude. Doing more of what he did against utd, like getting the flick on for richarlison's goal will help, but I'm still not convinced.
I am not sure Rashford has scored many more goals than DCL. Rashford has 7 goals 5 assists last season (one every 150 minutes) and 10/7 this season (one every 117 minutes). Calvert Lewin has 4/8 last season (one every 156 minutes) and 6/5 this (one every 146 minutes). Calvert Lewin is a little old (6 months older).
They are broadly similar stats, albeit that this season Rashford has kicked on another level. It is worth noting that he plays with Lukaku, Sanchez, Mata, Pogba etc who make and take many more chances. Calvert Lewin has played in an Everton team under Koeman who was sacked, Allardyce and then Silva when we were really struggling.
You also have to factor in, almost all United fans want to build their team around Rashford and believe he could lead the line in one of the best teams in Europe. I can't see how many on here don't think Calvert Lewin is good enough for a side that is a mid table team, aiming to break the top 6, when their records are very similar.