Diomande complements Mbappé better than Vinícius Jr because he understands positional rotations. When Mbappé drifts left, Diomande occupies the centre instead of leaving the box empty.
Vinícius wants to play to his own strengths rather than complement Mbappé, creating an imbalance on the left. His lack of pressing only makes things worse.
Diomande on the left, Mbappé through the middle and Güler on the right. Mourinho needs to prioritise what works for Madrid, not player egos.