If Chen can execute a 5 quad LP with good quality, no watering down the rest of his skating from start to finish, then his stamina is impressive. But as of now, he must sacrifice the rest of his skating, and jumps in the 2nd half to just get through a 5 quad LP. (He put 4 quads in the 1st half. At national and 4CC, his jump execution in the 2nd half just got worse and worse as he got more tired by the end of the program.) He is barely getting through a 5 quad LP with watered down transitions, and minor mistakes here and there, even when he is in top form. Most of other guys are also just barely getting through the rest of their programs. So I don't see his stamina as being better than other men in the top 6. (When men add more quads, the rest of their skating suffers because the stamina they have is limited and they can't improve their stamina significantly in a short time. Most men have to water down their tech in some other ways when they try to upgrade their layout, e.g. recycling old programs, or skate the same type of music or same choreography, or water down transitions.) He is nowhere near getting through a 6 quad LP even when he is in top form, let alone when he is not in top form or top condition under enormous pressure. I believe that's the main reason he gave a messy performance at WC. The boot problem was secondary and just made it worse. The thing is skaters only take calculated risk. They study their own protocols and their rivals' protocols. They try some risky jumps to test a new layout, but they won't stick to a layout that has proven to be not working. As of now, he has a 50/50 chance to get through a 5 quad layout with room for improvement. If he does a 6 quad or more quads layout, I'm afraid the chance of him being off podium will significantly increase.
I'm saying this as someone who really likes Chen. But I don't want to over-rate his ability and chance. (The other medal contenders' ability and chance is not better or much better either.)