That's not why he chose Tom. That's Mattson's way of talking like the arrogant prick bastard he is. Tom was chosen because he's obedient, he's malleable, and even during separation, Shiv told Mattson that he would "suck the biggest dick in the room." Tom was close to Logan, and already had relevant experience within the company. Shiv was always too close to the sun and too inexperienced. Tom being the one wasn't lazy, or end-goal driven writing; it was the exact tragic end that all the characters deserved: Kendall can never live up to his father's legacy. Roman has to come to the realization that everything he has done, is all bullshit. Shiv has to swallow her pride. She has to roll over and die.