In bridge, should a defender play differently with most, about half, or few of the partnership's points?
I don't think the number of points in your hand it the relevant feature here at all.

Essentially, you look at your hand, and see that you can easily take down the contract if you establish your 3 hearts winners before your opportunity to regain the lead with the KD is removed.

Returning a spade isn't going to help much as we're pretty certain partner isn't going to win that trick with his Jack.  As such, you have to forget the "usual rule" of returning partner's lead, which isn't going to help in the current situation, and just make the best play for beating the contract instead.  Partner has basically nothing, and you have an excellent defensive hand here: it's not up to him to dictate the whole play of this contract via his lead, just because of the seat he happens to be sitting in.