"I just need more effort on the hammer."

Yes, the amount of effort is "relative." Almost all of the flat surface of the rotor contacts the hub. That's a lot of area to collect rust that is holding the rotor on.

Mine required large amounts of PB Blaster in each lug hole, an overnight soak and serious 8 lb sledge slamming.

Before reassembling, makes sure both inside of rotor and hub are rust free and relatively smooth.

Bob