As someone who would drop Roy for Malan, this is correct. Roy and Bairstow have a lot of credit in the bank.
I was going to replace him I'd go with Salt or Jacks, they are more like for like. England have been at their best when they get the quick starts from Bairstow and Roy. Root comes in an casually bangs out a 100 and the middle order play around him. Not sure if Malan has it in him to maintain the momentum. He could probably probably a holding role like Stokes often did but Stokes is back. I think Root and Stokes means there's no need/room for him in the middle order.
He is a reliable backup, who can bat in the top four, but I just think England have thrived on the quick starts from openers. Jacks offers more spin too of course, so you could always bring in Brook at 6 instead of Livingstone.
The New Zealand series will be a good measure of where they are at with their thinking. I would assume if Roy does play and gets three low scores that'll be all anyone talks about.