It's really a combination of two things for me. This video didn't do a great job of showcasing him in particular I'll admit. 1. You don't need a spectacular nuke for him to be good. It's very easy to get him to 6 with a leader charge or Scenario (since he has 3 tags) and be able to kill two 6 power enemy units. That's him playing for 15 which is good. Anything above that makes him amazing. Even in a bad case of him only killing one 6 power enemy that's 9 for 10. That's not great but it's way better than the poor value case of something like Geralt. You'll almost always be able to kill at least one thing with Schirru (unless you're like me and boost him to 11 lol). 2. The other big thing is the threat of Schirru forces your opponent to play differently. They can't play into Schirru because they will just lose. It forces them to change how they are ordering their cards and boosting things and miss out on value pretty often. Some people forget to, or their deck can't play around Schirru (Heist Waylays for example), and you get a free win. So, you end up having a card that normally finds good value but has an insane ceiling that can win you games on its own. That's pretty good. As a couple bonus mentions, he's one of the only ways to get immediate control in the deck. Since you want ST units to trigger Harmony it's pretty much him or Brehen and he's more flexible with a better ceiling. Plus, you're playing Guerilla Tactics anyway to maximize Willow and he's the best payoff card for the other leader charges.
He's come in clutch for me a couple times. Funny, one time I was playing NG against this deck, I got shirru from bribery and was able to nuke his immune Saskia and 2 bronzes
