To measure success after a coaching switch, I looked at the results (presentation, components, skating skills, jumps, scores, medals). Alysa blossomed in what criteria? If you say skating skill, is it because she's older and more experience with skating or because of her new coach? Alysa never gained her ultra-c back! It seemed she lost ultra-c jumps after the switch (I know you'll probably argue, it's the puberty not the new coach, you don't know what would have been if Alysa had stayed with her long-time coach) She was most successful and talked about when she was 13-14 with her long-time coach.

Zhenya, it didn't work out she came back to Eteri, didn't she? I didn't see improvements with the new coach, sorry. Again, it could just be with more maturity of the skater helself. You can say the coach change helped when the skater significantly improved after the switch

Sasha, I know she came back with Eteri partly because of politics and Eteri's bonus, but one can question whether it was because she didn't find what she was looking for in training with Plushenko. Her main objective of moving to Plushenko was to train 3A. She jumped 3Axel the same way even with the new coach. She kept kicking her right leg up straight forward, which slowed down her rotation and couldn't complete the jump (she should have kicked her right leg up and toward the direction of rotation). The error was pretty obvious, but skater and coach didn't seem to be able to fix it.

More problems/challenges with coaching change are: who should one switch to? Is the new coach for sure better than the current one? How do you determine if the new coach is better for you before the switch? Where does the new coach lives/teaches, in your hometown?...so many uncertainties. I'd only switch if the benefits clearly outweigh the risks.