I think what OP meant is that this logically implies every query must touch all the data (or else you could infer information from data access patterns) at which point is it really a database anymore as we know it?
You could run statistics on data or do a grid-based simulation.
Running a neural net would be almost trivial.
General purpose code is extremely difficult to adapt, since it loves to branch based on data.
All you have to do is multiply each weight and add up each node.
Pure bulk arithmetic is both simple and a perfect match for FHE.
Hell, I’m not an ML practitioner and I almost never use python, and yet it took me maybe a day or two learn enough about covnet training to detect my dog on a home security camera.
If you mean is it useless as a replacement for the mysql backend of your php app, the answer is yes.