He's exactly what his father wanted him to fight against.
He was party to the killing of what his father wanted to fight against--his wife's own father. He was never as good as portrayed or as he saw himself. It's the deception of the camera. He'd always wallowed in the belief that he had no power and needed to climb up. He said so himself--"Even spiders need silk to climb up," so what shouldn't he? His silk was his wife and yes, the relationship was good, so he had guilt about that, but that didn't stop him from doing what needed to be done for climbing up. His next silk was the Princess and yes, the relationship wasn't that great but that didn't stop him from being part of her plans. Now, he didn't want his status to be ruined any more (by revelation of the affair and thus exposed him as the adulterer, not his "dead" wife and possibly starting an investigation). So he did what needed to be done, gave the idea to his Princess to marry Li. It was all about him, always. I concur with your reading of his character.
Those two young actors playing Kid Emperor and Kid Duke Su are so good. The voices, the stance, the way they looked at each other. Someone has coached them well.
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He was never as good as portrayed or as he saw himself. It's the deception of the camera. He'd always wallowed in the belief that he had no power and needed to climb up. He said so himself--"Even spiders need silk to climb up," so what shouldn't he? His silk was his wife and yes, the relationship was good, so he had guilt about that, but that didn't stop him from doing what needed to be done for climbing up. His next silk was the Princess and yes, the relationship wasn't that great but that didn't stop him from being part of her plans. Now, he didn't want his status to be ruined any more (by revelation of the affair and thus exposed him as the adulterer, not his "dead" wife and possibly starting an investigation). So he did what needed to be done, gave the idea to his Princess to marry Li. It was all about him, always. I concur with your reading of his character.