Gu Qingzhi/Shen Xihe single-handedly ended the entire 7 man strong heir apparent run. Like all the princes had a chance at the throne till she happened.
In her early form, she took out Changqing who was widely expected to ascend once the sickly crown prince died. She dies first round, his momentum dwindles and then 2nd round he forfeits magestically for her.
Everybody else has a theoretical chance but she realistically snuffs out that pipe dream, with heavy handed help from the crown prince himself.
The Crown Prince desperately wants to be Emperor and is doing everything to stay alive and ascend the throne and have a historically impressive reign! He falls fatally in love (in ways only Changqing can accurately explain) and all he does after that is prepare the kingdom for HER reign!
The total and quiet decimation of such a well stocked Princely generation could fit into a more malicious revenge themed drama with ease but instead Shen Xihe plays it out like a mildly thrilling chess game.
We must pay respect to the woman who pulls off the race to ascension with such grace and style, a femme fatally for the ages, the incomparable, beautiful and wise: Previously Prince Xin's Consort Gu Qingzhi, Di daughter of the illustrious Gu Clan; now the Di Daughter of the Military Shen Family, former Commandery Princess Zhaoning and Crown Princess, Grand Dowager Empress Shen Xihe.

But it kinda funny Xioa Hua Yong has been passed over for the throne twice. The father Emperor passing the throne to his baby grandson is really forcing his sons to do what he never could do.

The Emperor is a weird character for me. I still had him pegged as a secret villain to the end but he ended up being just a human, with some darkness but majority good parts. I feel sad that his love for Huayong was probably mostly guilt and maybe he knew deep down the poison was from the grandmother, knowing he made "his mother" poison her only blood relative would have really hurt too and knowing, if he had let Huayong be Emperor, he probably could have protected him more and never let him get poisoned.....

But of all the cdrama Emperors I have watched none has raised more humane, sane and actually heir worthy Princes. The sons were competitive but they all genuinely liked and respected each other to a large extent and saw themselves as actual brothers. They all pulled their punches with each other and they never thought to take each other's lives or even reputations with ease. Death and destruction was a hard to take last step.

The father deserves recognition for that.