The Mandalorian season 2 finale featured a surprise cameo by young Luke Skywalker played by digitally de-aged Mark Hamill, but the show should've just cast Sebastian Stan for the role. It's true Star Wars has used the de-aging technology in the past, the first time in Rogue One: A Star Wars Story and most recently in Star Wars: The Rise of Skywalker. Despite that, Luke's appearance in the Disney+ show looked far worse than his predecessors.
Din Djarin's mission to reunite Baby Yoda with the Jedi culminated in The Mandalorian season 2 finale titled "The Rescue." Following Moff Gideon successfully kidnapping Grogu in "The Tragedy," Mando assembled his own team of allies to help him retrieve the Child from the villain. In the end, they were successful, but the reunion between the father figure and adopted son didn't last long as Luke came just in time to pick up Baby Yoda and start training his ability to tap into the Force. Since The Mandalorian is set five years after Return of the Jedi, the show had to be feature young Luke to fit the timeline.
Instead of hiring a different actor to play the role, however, The Mandalorian opted to bring back Hamill in the role, who had to be de-aged digitally to recreate the character's look from that era. Unfortunately, the end result wasn't all that good. Granted, Star Wars' previous use of the technology was also rough, but its limitations were more underscored in this instance as young Luke is more prominently featured. It's also worth noting that budgetary constraints also contributed to the matter. Given this, it would've been best for Lucasfilm to simply recast the role with Sebastian Stan, who looks so much like a young Hamill and can no doubt deliver a believable performance as Luke Skywalker. Admittedly, there could be a couple of factors why The Mandalorian opted against tapping Stan to play Luke in the season 2 finale. For starters, Lucasfilm may have been burned by recasting the Star Wars legacy characters by the reception to Solo: A Star Wars Story. Perhaps Stan wasn't available, either, seeing that he's busy with Marvel Studios' The Falcon and the Winter Soldier and other projects outside of the MCU.
That being said, casting him as a real person and not a de-aged Luke Skywalker could've proved to be worth it. As exciting as it was to see Luke in The Mandalorian season 2 finale, the poor CGI on Hamill undercut some of the emotions of the scene. He had several close-up shots and every time he spoke, it looked so fake that it was uncanny valley creepy. Stan playing the part would've resolved this matter; it would've given Lucasfilm more opportunity to get him involved in the sequence instead of standing so stiffly with such unnatural facial movements. It also would've fully opened up potential storytelling featuring Luke during this time period. Since the sequel trilogy never really delved into Luke's attempts to rebuild the Jedi Order leading to Ben Solo's fall to the dark side and his exile in Ahch-To, there's a lot of untapped narrative they could tackle with Stan in the role.
What sets this particular recasting apart from Alden Ehrenreich as Han Solo is that fans are already on board with the idea. Things were different with getting another actor to play Star Wars' scruffy nerfherder as there was staunch opposition to Lucasfilm making Solo in the first place. In The Mandalorian, however, the story demands the presence of a young Luke, and fans have long since fan-cast Stan in the role. Since Stan's already under the Disney umbrella thanks to his MCU stint, it's safe to assume that bringing him into the galaxy far, far away wouldn't be difficult.