Do you watch this show and skip the dialogue here and there? First episode Jon point blank states that Lord Karstark and Umber would have been executed had they been alive. He tells Theon the only reason he's not dead is because of what he did for Sansa. Tarlys would have been executed, and I doubt Jon would have given them a way out. Had the Tarlys betrayed a House loyal to the Starks or the Starks themselves, they would have died. It's no different than the Karstarks and Umber.
So is your problem the method of execution? Because if it is, Drogon killed them in seconds flat. Hanging would have taken longer, and only beheading would have been quicker. Sure as shit beats eaten alive by dogs though right? Or do you think Jon left Ramsay for Sansa to have a chat with and didn't know she was going to kill him?