Why is that weirder? The people writing scientific software are, by and large, less good at writing software than people who only specialize in software development. I’d expect there to tons of terrible engineering practices in an old code base like that
Well, yes and no.
Quantum computers will likely never beat classical computing on classical algorithms, for exactly the reasons you stated, classical just has too much of a head start.
But there are certain problems with quantum algorithms that are exponentially faster than the classical algorithms. Quantum computers will be better on those problems very quickly, but we are still working on building reliable QCs. Also, we currently don’t know very many quantum algorithms with that degree of speedup, so as others have said there isn’t many use cases for QCs yet.