On top of my head:
Sasha Cohen left Tarasova, bad decision.
Sasha Cohen left Robin Wagner, not bad decision.
Michelle Kwan left Frank, bad decision.
Johnny Weir left Priscilla Hill, good decision.
Just to make it more accurate.
Sasha's mother arranged for Sasha to train with Tarossova. At the breakup
Tarassova suggested Sasha train with Wagner. At the breakup
Sasha returned to Nicks. She earned a Silver medal at 2006 Olys.
Priscilla Hill went to Tarassova to ask her to train Johnny Weir for a few months.
Tarassova after a short while left Sasha and Johnny to go to Russia.
Johnny remained with Hill until they reached an agreement and he looked for
another Russian coach. What will happen at Worlds, we don;t know.
Just before 2002 Olys, Kwan shocked the skating world when she left Frank and Lori with no reasons given. She went on to win the 2003 Worlds.
One can only give an opinion on whether these changes were for the good or not.
Personally, I do not put total blame on coaches. It's the skater messing up, too.
Rumors about Mao and Rafael would only be my opinion and not important, and we'll see how Kimmie and Callaghan do for the short time at Worlds.
Joe