This! Exactly This! Aligns very well with my experiences too, especially getting seating together with clients or colleagues on separate bookings, and when I have to change routing/cancel legs on the day. And totally agree this is one of the reasons I pay for J travel domestically.
You lost me at "getting seating together with clients or colleagues".... I get cross when work books me on the same PNR and I do get seating next to clients or colleagues. Oh the humanity