Legality was the question, and as explained above the ‘legality’ is with the interpretation of the rules, particularly 1.450.
The UK CAA has provided an interpretation such that any other Authority, Operator, or Commander might be challenged to justify an alternative so that in the event of an accident, the lawyers would not be knocking at their door; now that is ‘legality’.
I prefer to think that the guidance material provides a basis for a Commander to judge a safety margin for landing and thus be comfortable with his/her responsibilities within the rule – but s/he still has to complete the ‘plan’, and that activity also requires experience.