What I observed from afar was that Gannon at Motherwell has caused quite a fresh breeze. Not everyone can use his special way is clear to me. But it worked for other clubs. Just not at Motherwell. Whatever. But I would not generalize that always bears the blame Gannon. He's have a line manager, not everyone likes, or not good for some clubs.
You will laugh but reminds me in some way to Van Gaal at Bayern. Only Van Gaal is much more difficult than Gannon. In my opinion.