Should canned fish be flaky?

Fresh fish is considered ready for serving at 60-65°C (plus minus a bit, depending on what kind of fish, cut, personal preference etc.). At that point, fish will fall apart into moist flakes if pressed with a fork, but not crumble on its own. Heat the fish further, and the proteins will denature in a way that the fish is perceived as tough and dry.

Safe canning for non-acidic protein-based foods requires temperatures of above 117°C, in practice up to 130°C. This is necessary to ensure food long-term safety and to destroy heat-resistant pathogens like the infamous C. botulinum.

In short, you can either have perfectly cooked, juicy and tender fresh fish or a shelf-stable product. They are mutually exclusive.
Your canned fish is perfectly fine for canned fish, not a bad batch, but simply can not have the taste and mouthfeel of a freshly cooked à point mackerel.