Malan's record is undoubtely exceptional, but he is not a great slow pitch player and has never really excelled against spin, and there is an argument that the risk of him getting out before his rate starts to catch up outweighs the benefits of him being able to go deep. In normal circumstances, I would say yeah, sure, you need someone in that Amla/Williamson role but when we have the depth of batting options that we have, it may be that he ends focussing on the longer formats.
I tried to put my squad together. I went for:
Jason Roy
Jos Buttler
Jonny Bairstow
Ben Stokes
Liam Livingstone
Eoin Morgan
Joe Root
Sam Curran
Chris Jordan
Adil Rashid
Jofra Archer
Dawid Malan
Saqib Mahmood
Moeen Ali
Matt Parkinson