It would make more sense for Tai Lung to be the main antagonist of the franchise rather than Lord Shen because the former appears in EVERY canon media of the franchise.
The main protagonist of the franchise is Po, and Shen is the one who is directly tied to him, while Tai Lung is tied to Shifu and Kai with Oogway. Shen's actions are what caused the domino effect for Po's life as well, and is a dark reflection, with Shen unable to move on from the past, while Po did. Both are also warriors of black and white.
Screentime VS Story Relevance. Lord Shen has arguably the biggest influence on the story as he more or less caused Po's life, while Tai Lung is just the first villain he faces, even if he has more screentime.
@WowVerySurprising in my opinión Vader is the main antagonist of the original trilogy, Dooku of the prequel trilogy. And Palpatine is the overarching antagonist of the entire franchise
