I doubt that it was a mutual agreement. Usually change is when someone is not happy. Either Tutberidze kicked him out, which I think is not very likely, or he was not happy with his training conditions. He may not want to complain loudly because that would damage the relationship with Tutberidze, and he will be seeing her in the future frequently at the competitions. Tutberidze has too many skaters, and quite a few of them pretty succesful within their age group, but that means that they all need their time with her. Goncharenko has Elena, Voronov and the rest are B level of skaters, so both Elena and Voronov will be able to have plenty of individual attention. If Tutberidze had 25 skaters, how many hours of one to one per day she could give him?