There can only ever be one reality, and so there can only ever be one correct theory of reality.

I disagree with this. A theory is basically a model (or pertains to one). Models by necessity leave out details of the thing they're modelling (if you disagree, then the best model of reality is simply reality, and we already have that). So depending on which features of reality you think are relevant, you can have multiple models of reality bringing out each of those features. The theories based on those models will sometimes make different predictions, but if they're good models they'll agree most of the time, and you make predictions using the model that makes those sorts of predictions correctly most of the time.

As an illustration, look at maps of the surface of the Earth. There are multiple projections based on preserving different relevant information. If you want to plan a sea journey, you use one; if you want to plan a land journey, you use a different one. A globe represents both more accurately, but is harder to carry around / print out of a computer.

Surely our models of physics can have the same sorts of properties; what allows you to make predictions about gravity may not be the same model that allows you to make predictions about electromagnetism.