Funny. In the Final Boss fight in the Star Wars MMO against Darth Malgus You need to kick him off the level to kill him, because he won't take any more damage at a certain point. They later patched it so that You could kill him with damage because so many players had trouble kicking him. It's sad that kicking a boss off a ledge in Destiny is considered glitching - it would be a lot cooler to see it as an alternate way to victory. But I can of course see how it is a lot easier ("cheaper") to kick both bosses off the ledge rather than kill them.