I agree. General intelligence, to me, is defined as the ability to create a greater intelligence. An ability that's hypothesized for humans, but yet unproven. Therefore, on the cusp of general intelligence.
Define "greater". And since your definition is recursive, define your base case.
I'll suggest that "intelligence" is about how much information you can extract from a given set of data. And since information theory says any given set of data only has a limited amount of information in it, this would imply that "intelligence" is not potentially unbounded but is on a scale of 0%-100%.
(The nuance is what Yudkowsky et al. tend to write about.)
second edit: "Can we actually change that en masse?" is the most interesting question.