I have a problem with my in-law . . .

[the phantom]

passing the sceptre to his heir (Míriel) before his death? Would this not have saved Númenor from the machinations of Pharazôn?

I think he did pass the sceptre to Miriel- but it still didn't stop Pharazon. From Akallabeth-

But Pharazon took her to wife against her will...And when they were wedded, he seized the sceptre into his own hand...