I think this link says it better than I can - http://www.aikiweb.com/wiki/generalv...#takumusu_aiki
The last line of the definition - "Once one has internalized the kihon, it is possible to generate a virtually infinite variety of new aikido techniques in accordance with novel conditions." - identifies the basis of the kata/randori approach to training. Regardless of what method one uses whether circular or linear or a bit of both, without kihon there can be no spontaneous manifestation.
The original question as far as I saw it was "How is this aspect of aikido dealt with in more systematic approaches to teaching?." Imho it has been well answered by a few people from at least 2 systematic approaches as far as I am aware.