Without wishing to denigrate the enthusiasm of most young FI(R)s and FIs, it is perhaps only because flight instruction seems to be widely viewed as merely a convenient method of pre-airline hours building rather than as a profession in its own right which allows such low-quality people as you have experienced to cause these problems.
In the RAF, only the most able are 'creamed off' for QFI duties before completing an operational tour; the vast majority of QFIs are experienced pilots who are selected for instructional duties only after demonstrating that they have the necessary qualities to fit them for the responsibilities of the QFI role.