I'm not promoting any theory whatsoever on this TU-154 accident but, FWIW, over the generations of jet airliners some T/O config warnings have been better than others - both in terms of the parameters covered and the method of detection. They all try to monitor the deployment of high-lift devices, of course.
On the B707 (first flight 1955), a first-generation jet, the system looked only at the position of the flight-crew's selector lever. The single lever controlled the trailing-edge flaps and the so-called leading-edge devices (Krueger flaps).
On the VC10 (first flight 1962), a second-generation jet which was outlived in service by the B707, the T/O config warning system used sensors on the leading-edge slats and the trailing-edge flaps themselves.
On early B747s (first-flight 1969) the extension of the leading-edge slats was not locally monitored by the T/O config warning, That, and crew error, led to a fatal accident in 1974:
https://aviation-safety.net/database...?id=19741120-0
None of the above systems monitored the degree of slat or flap extension, which on most aeroplanes is variable to suit the conditions.
Where does the TU-154 (first flight 1968) fit into this pattern of development?