I don't think Tarkin ruled over Vader absolutely, he was just in control of the Death Star and Vader respected that. Remember Tarkin/Anakin go back to the Clone Wars.
If Vader felt that Tarkin was overstepping I'm pretty sure he would throw him in the bushes, even when he stopped choking the other cac Vader was quite casual "as you wish
", he was just having fun out there.
I see it was Tarkin being the Iovine and Vader on some Suge Knight shyt - yeah Iovine owns the label (Death Star) and Suge respected that because it brought in the money, but Suge had power on another level.
It's also comparable to BANE in the last Batman movie, when that rich cac starts cussing at him and Bane just puts his hand on his shoulder.
Rich dude: "....I gave you a fortune
"
Bane: "And you think that gives you power over me?
"