The whole process of cooking does not always start by turning on the heat. It often starts where the ingredient sits and gets ready for the heat. This would make the difference when it comes to texture both in firm or soft.

Take a frozen chicken drumstick for example, when you drop them into a boiling water while they are still somewhat frozen you will get a firmer texture vs when you allow it to completely defrost (softer texture), combining with what heat setting you have them cooked at.

Also when it comes to fish, salmon, there is a difference in choosing fresh vs previously frozen. They don’t come out the same from the oven because one has been frozen (although it is thawed out when cooking) and the other is fresh (never been frozen). The tenderness in the texture on the fresh salmon is far superior and juicy then the previously frozen one.