I don't agree with your interpretation or reasoning that punctuality means a T is ruthless. It's not "ruthless" to the next client to start on time rather than late (or the next one, and so on). Starting and stopping on time is one way of "containing" the session, which increases a sense of safety and security. And doing this consistently means that a therapist is consistent, a virtue that is often heralded here. Giving more time on some sessions and not others would be changing the rules without consulting the client.

And starting and stopping on time is just good business ethics, in therapy and in many of the professions. If a T is late to her next session because she ran over with the previous client, then she'd be unprofessional.