The binding blade chose Roy, so it could make sense that maybe Eckesachs chose the kingdom of Bern's family, Hartmut's descendants, to wield it and nobody else. Roy and his crew canonically get it, but the blade didn't choose them so it won't let them wield it.
So it would only be balanced towards new players who don't early promo Rutger, and even if they wait till chapter, say, 14, that's still like 10 chapters of the game with a infinite use 22 might sword. Anybody who plays it again will promote Rutger there and snap the game in half.