I'd take issue with it being the only use case. There are things QC is useful for beyond factoring. Its just that all the use cases (including actual factoring) are so far away from being reality that nobody would invest if they were being honest about the time horizons.
OK, to be fair I exaggerated a bit in my previous comment. Looking at lists of known quantum algorithms, I just don't see many that have practical use cases, and even less that could possibly be implemented in a reasonable time scale.
I feel, and that may just be a feeling, like Shor's algorithm and its modern variants are the only serious applications so far.
Usually the best alleged application is using them to do physics simulations that wouldn't be possible on a normal computer. Its a bit unclear precisely what that will open up, but normal computers opened up a lot of applications by being able to simulate classical system, perhaps QC will do the same for quantum physics things.
You're right that most of the other algorithms are pretty useless. Shor and Grover are certainly fascinating intellectually, but i doubt would be particularly useful (shor because everyone will switch to pqc if qc ever becomes relavent and grover is too slow to ever be useful)
And D-Wave's quantum annealers have no path to run either Shor's or Grover's algorithm, so far there's no evidence they're any faster than simulated annealing.
