"most important organization in Australian basketball"
People continue to identify the health of the sport with the health of one competition. Health of a sport is usually measured by participation levels in the population and results on the international stage.
Population participation in organised basketball in Australia has borne no relationship with the popularity, size, viability or public profile of NBL over the last 25 years. Organised basketball participation has grown in line with population growth throughout that period, based on Australian Sports Commission and Australian Bureau of Statistics data. In the meantime, the NBL has seen booms in popularity, busts in popularity, variable profile through TV and media coverage, multiple team failures and multiple new teams.
I'll accept that the question of whether participation might have fallen if the NBL ceased to exist, is an open one. But so is the question of whether the NBL would have ceased to exist without Kestleman's purchase of the league.
One area where I think the NBL has become more important in recent times is international performance, with the change to the FIBA qualification process. The NBL now delivers whole squads for that process, which was not the case for the decade or so beforehand. That has made the NBL more important to the health of the sport itself, through a more direct contribution to Australia's international results.
Kestleman has changed the NBL significantly and it's probably overall for the betterment of the league. In saying that, I note that we don't know if the league today is truly a commercially sustainable proposition.
It remains to be seen whether that betterment of the NBL leads to any improvement in the health of the sport of basketball in Australia. It's quite possible things like introducing 3x3 will have a greater impact on participation than improving the commercial viability of the NBL. Internationally, the performances of Australian players in overseas leagues will have more impact on the international results that matter, than the NBL's success or failure.