"Hinder for a single round" is your problem here. For the right foe, being immobilized is effectively incapacitated - many foes don't have powerful ranged attacks. And 'single round' is 'until I choose to stop'. The ability just keeps going as long as you keep maintaining it.
Let's say you'r a 15th level barbarian up against an ancient red dragon, and your charisma is 10.
You still have a 25% chance to affect him. And once you affect him, if you can pull back to 125 feet with the right angle... the fight is over. You literally have as long as you want with that sucker sitting in his corner getting slammed by whatever your buddies have range with, with zero chance to break free.
Personally I think that's worth a crack instead of some comparitively small portion of his hitpoints.
One correction, the effect ends if the target is more than 60 feet away from you, so your example would not work. But even at 60 feet it does limit a dragon to just its breath weapon.
You have given me some compelling arguments, I think this ability is probably still pretty situational, but might still have some good kick to it.