grammar - The usage of "was always"

It is grammatical. To me it seems less likely than "has always been", because it implies that the possibility of baking cakes is no longer present.

But a case where it would be natural would be if the very thing which is no longer current is finding it hard to bake cakes: if they go on to say that since some experience they now find it easy, then the simple "was" will be quite natural.