Physically, he's average at best, which limits his productivity and output in the league. He's only 22, but he has to work really hard and focus on his body.
He can get stronger yet increase or maintain his agility and balance and technique. So far under EtH, the team can be very transition heavy and quick, which is not exactly his strong suit.
He does provide a very good link up in the attacking 3rd and can score with well taken goals. He's not necessarily a match winner who will do something out of nothing, especially when it comes to creating one's own shot.
There's a place for him in the team, but compared to his transfer fee, it's not good enough. Eriksen will have first crack at playing for Bruno, as has been the case throughout the season where Bruno goes wide and Eriksen assumes the 10 position.
With Ronaldo having difficulty scoring or providing anything besides a goal threat, it forces Marcus to stay at his best position which most of already known as a left forward who is more intersted in scoring first than assisting and linking up for the greater good of the team. Seeing Elanga play in the right over Sancho against West Ham confirms the physical understanding from EtH that is need against many PL team and the fact that Sancho isn't physical enough to really cope with it.