I think the game was fine to start Ilaix. Pedri needed rest and Ilaix has been our most played alternative midfielder over the past month. And has played well.
Who else would you play? Puig? Pjanic? Roberto?
The problem wasn't Ilaix against Granada, even if he had an average/poor game. It was the whole team. The team Lacked intensity, individuals had no impetus to do anything but try and find Messi, and the defence cost us two goals on two attempts.
But he was fine for the majority of the match and got lost when Granada scored as the whole team got lost. Koeman got lost and got himself sent off.
Was lower than my expectation but no point to single out. He will come again the wiser.
A last point that Ilaix might have been fasting which would have affected his energy output. If he is/was then better wait until a 9pm game where he can hydrate just before kick-off or half-time. That's on the management to know.