If the F-35 is operating within small drone range, it's probably detectable on infrared tbh. If it's a larger drone, then there's not really much of an advantage of launching it by F-35 because you'd probably be outside of radar range anyway. The F-35 is most useful when it IS accomplishing the role of CAS because it has the benefit of a pilot.

As it stands, I feel like the primary role of jets today is to maintain aerial superiority to drop heavy bombs (which are far cheaper than building an equivalent drone).