Maybe the "percentage" definition fails the logic test somewhere? But the purpose for that expression is to affirm the FULL humanity and FULL divinity of the God-man.
"Truly" doesn't convey the idea of "completeness" very well, in my opinion. "Fully" does a better job, I think. Plus, "truly" seems to me could include some kind of "ethical" angle, which only inserts an unnecessary wrinkle.
The Second Person isn't half-this/half-that, or some other percentage distribution. His divine nature is complete and entire, and suffers nothing diminuted or increased by the association to it of a complete and entire human nature--a properly subordinate nature that also retains its own exclusive properties, and is not transmuted by its association. "Without conversion, composition, or confusion," is taken from the Definition of Chalcedon, AD 451.