I think you're seeing the inherent weakness of a non-thoroughly plotted magic system. The more power that Xerath gets portrayed to have, the more the writers leave themselves open to people looking back and going "Hey, wait a minute, if he can do X, why didn't he do it here where it would have totally solved all his problems?"
The answer to those questions are almost always a variation of either "He didn't think about it" or "His arrogance got in the way of him making the obvious move." Which, basically, both make the character look like a complete idiot, whether or not the character had been portrayed that way leading up to the event. The honest answer is usually, the writer didn't think about it, or made up this cool move later without really thinking about how that magic would shape the story and world.
Which, since I usually over-analyze everything to oblivion and back, is why I personally prefer toned down subtle magic or very rigorously plotted magic. Both of which can fall into the same narrative trap, but are less likely to do so. The only real satisfactory way to handle high powered non-thoroughly plotted magic is to just ignore the problems when they come up. Which I personally find very hard to do, but maybe you can.
is still strongest being imo.
