Sorry but that's a poor comparison. There's a vast difference in punching power between a heavyweight and a welterweight (or middleweight in Benn's case). You can dominate a heavyweight fight for 11 rounds and then get caught by one big shot that KOs you. For example, Fury mostly bossed Wilder and then got caught by that massive shot that he probably didn't have any right to get up from. Ruiz might have been out of shape but he's still got good hands and can land a heavy punch, particularly short hooks.
You might not like it but Joshua fought the smart fight. He's got much longer reach and is a technically superior boxer to Ruiz, so he played to those strengths by keeping Ruiz at distance and landing shots behind his jab. He did the same thing in his fights against Whyte, who is a dangerous boxer at close range like Ruiz. Boxing isn't just about knocking someone out, if it was there wouldn't be judges or a scoring system and we'd just let the two boxers fight until one of them was KO'd.
