So this is my take on LYB's decision to field LD as the second MS player:
After the loss to Japan in the Thomas Cup, LYB was criticized for not fielding LD as the second MS player. Fielding LD as the second MS player at the Thomas Cup would have ensured China would get a win in the 2nd MS game.
I'm going to assume WZM and Tian Houwei are healthy. Here is where it gets interesting. LYB probably didn't feel confident that WZM and Tian Houwei could get a sure win over Korea's second MS. And after the Thomas Cup loss, LYB didn't want to be criticized for not fielding LD and wasting him on the bench. So LYB opted to field LD second this time around for the guaranteed win in the second MS match, and lost the opportunity to use WZM and Tian Houwei.
Ironically, what he didn't consider was the strength of Japan's MS and Korea's MS. Japan MS >>> Korea MS. Lee Dong Keun is ranked 34 and IMO, is nowhere as strong as Kento Momota. It's conceivable that Kento Momota could beat Du Pengyu at the Thomas Cup, so LYB should have fielded LD second at the Thomas Cup. LYB had too much faith in Du Pengyu's ability.
In this Asia games, LYB didn't have enough faith in WZM or Tian Houwei. WZM is ranked 6th now. I think WZM isn't a guaranteed win over Lee Dong Keun, but I would put WZM at 70% to 80% likelihood to beat Lee Dong Keun, even though Lee Dong Keun is on home soil.
LYB should have considered Hao Guan almost a sure loss against LHI. LHI is probably the second best singles player on the Korean national team, even though his ranking says otherwise (just like LD is probably still the best player for China even though his ranking says otherwise). Everything went against LYB's plan when Chen Long lost.
The funny thing is, LD's ranking should have been higher but he lost to Jan O' Jorgensen at the Japan Open. Korea can send a thank you card to Jan O' Jorgensen for knocking LD out at the Japan Open and keeping LD's ranking lower.