Harness racing is a game of loyalty and mateship first, business second in my books. (I'm not saying people aren't entitled to try and earn money)
Yin and Yang - good business decision changing trainers (perhaps), poor morals (you may disagree).
In this scenario it's not like Excel Stride was performing poorly either. At the very least you have to feel sorry for Heath wouldn't you?
Side points:
Trainers are more than entitled to train any horse they're offered.
I'd hate to be Sam Nati - he is expected to be superman.