I think that theory holds even less weight than the hyperdisease theory of extinction which even its proponants say has no, nada, 0 evidence.

Evolution favors whatever increses the chances of reproduction in a particular environmental niche. Sometimes it's speed, sometimes it's size, sometimes it's claws or fangs. Saber tooths arose several times only to disappear, flight has evolved at least 4 times, giganticism has come and gone several times, creatures have left and returned to the sea many times, many animals have evolved similar body shapes for similar life styles. Intelligence has risen only once. Considering the other multiple evolutionary events arose with potential niche competition it seems the intelligence niche is indeed a rare combination given that it was not occupied in the absence of competition.

Regards,
Mark