I think that he's referring to the poor endgame kinematics of very large missiles. It's hard for a missile as big as S-200 (and, for that matter, likely 40N6) to keep up with tactical aircraft, think F-15E or F/A-18. The only realistic targets are bombers and ISR aircraft, and the former have evolved somewhat out of the reach of S-200 (B-1B flies below the altitude floor, and B-2 has good LO characteristics against Square Pair).

Furthermore, truly fixed systems like S-200 are extremely vulnerable to cruise missiles, especially given S-200's engagement floor. S-200 isn't truly viable anymore, with even S-75 and S-125 surpassing its usefulness.