Just picked up an Apple leather case and I initially thought I had a dud button on the case. But no, I took it off and the button is definitely mushy at the lower end, and more clicky at the top. In fact, if I press the bottom of the button it doesn’t work at all. The volume buttons are perfect, however. It also seems to be a bit more pronounced once inside the case. I’ll see how I go but I might return it - a phone over £1000 should be perfect.
If the bottom of the button doesn't work at all, then it's defective. I would return it versus just considering it as you stated.