I think the substitution is accurate. They say aikido has 3000 techniques. My theory is that there are only a handful of aiki principles out there. Waza is therefore a permutation of different principles combined together to make the 3000. Although the outside form looks different for different techniques, these are just made up from the same underlying principles. IMHO, the goal therefore is not to concentrate on mastering different waza but to understand the common underlying principles for these. 2 techniques may look different in form but the principle is the same.