I don't believe anyone doubted that Rakitic couldn't be DM. I did see workrate though. He was out by his goal-line trying to defend, always confronting the man on the ball in midfield, and whenever he could've provided something defensively he did (2nd half was more about either Croatia being in possession or Brazil passing around the back). If he had Busquets or a DM behind him, being 'defensively secure' wouldn't matter at all since he'd just be adding to our currently weak pressing game.
I wasn't impressed today but I've seen enough of him to know not to take this match as a judgement for him. You're barely getting a glimpse of what Rakitic's game is being chained down in that static defensive role. I hope he gets a better chance in the next few games and does well.