Deutsch's algorithm is not faster on a quantum computer, Deutsch's algorithm is only possibe on a quantum computer.
A classical computer cannot perform Deutsch's algorithm, a classical computer can only simulate Deutsch's algorithm. Forget about speed, more fundamental is that we are performing a type of computation that can never be performed, in any amount of time, by any classical system.
Consider the case of two possible evaluations, $f(0)$ and $f(1)$. In any classical computation these evaluations are mutually exclusive. We can design a classical system that evaluates $f(0)$ or $f(1)$ probabilistically to simulate Deutsch's algorithm, but any given evaluation is either $f(0)$ or $f(1)$. Evaluating one means we did not evaluate the other.
In contrast, Deutsch's algorithm is not evaluating $f(0)$ with some probability $p$ and $f(1)$ with probability $1-p$, this is only the outcome that we can simulate classically. In Deutsch's algorithm the two evaluations $f(0)$ and $f(1)$ exist simultaneously (in superposition) and interfere with each other.
I suggest forgetting about performance until you have a very clear understanding of the fundamental difference between a quantum algorithm and a classical simulation of a quantum algorithm. In other words, until you have convinced yourself that Deutsch's algorithm can never be performed by a classical computer.