Ever try that with a pork shoulder? I let mine rest for a full two hours wrapped in a cooler once. The bone just slid right out clean. Makes all the difference with those bigger cuts.
Honestly, I saw a video where a butcher explained that a longer blade helps with the initial deep cuts through a big roast like that. It keeps you from having to saw back and forth, which can tear the meat. A sharp, thin knife just follows through in one clean motion. That clean cut probably helps the texture later on, too. It makes total sense why it worked so well for you.