I used to hold Taejong in high regard

But looking back at him as I get older, I find him so cruel that my opinion of him has diminished.
To make him king, his wife's four brothers risked their lives to support him; he could have simply exiled them, but instead, he executed them all, wiping out their entire clan. Then, under the pretext of strengthening royal authority, he executed and exterminated an innocent in-law, causing his own daughter-in-law to faint from shock.
At the same time, he cherished and overlooked a scoundrel like Yi Suk-beon, only eventually settling for exiling him later on.
There are cases, like Emperor Taizu of Song (Zhao Kuangyin), where a ruler persuades meritorious officials to relinquish power in exchange for wealth and honor. I don't understand why he had to be so cruel and kill them all. This became a major issue later on: when Danjong ascended the throne at a young age, there was no maternal relative power base left to protect him because of Taejong's purges.