Depends on how the window was set. If that is the reveal of the window and the contractor set it with a new construction nailing flange, the window is basically done. I would probably still tape off to the trim and install some sealant in that gap, but if the window was flashed and set via new construction application, he is mostly correct.

There biggest failure was to communicate what the outward appearance of these 2 products would be when sitting side by side. The problem is doors go in like like Old construction which have no nail fins and the casing overlaps the frame. In New construction the frame sticks past the sheathing and casing butts up to the window. If this window we’re to have a vinyl casing available (which many don’t) the Windowbwouldnhave to be downsized. The window could have and still can be set with out nail fins. and pushed inward , then put casing overlapping the frame. The nail fins would need to be cut off .