I think I shared this before: I use nested ticketing a lot. I once got a call from KLM that my bookings were flagged based on this behavior. So I told the lady on the phone: "Are you calling me to tell me I need to book 50% of my nested ticket on another airline? Are you sure that telling me to take 50% of my business elsewhere is helping you in any way?". She said she would talk to a supervisor, never heard back from them.

The thing is, there is very little the airline can do. You book two tickets and per ticket you accept the T&C. But you are not accepting any T&C spanning across multiple bookings. As long as you respect the T&C per ticket (like flying the legs in order), the airline cannot do anything about this.