That would do, yes.
Wardrobes are tricky because they often sit on carpet in a bedroom and floors are not always level, especially in old houses where things have moved a bit.
I've made a number of wardrobes over the years and have always had this problem.My first domestic piece here will be a wardrob eand I shall make a base unit that sits on adjustable feet. Hafele do one that can be adjusted from above through an access hole. That way the plinth can be leveled up in situ, stood on a board, and adjusted even after the doors are hung. It's a system that works well.
I don't see how your cutting can be 4mm out. But the flexibility of an MDF carcase of that size can easily allow it to be 4mm out.