One of the arguments I have had with the two earlier shows and continue to have with the present one is with the concept of race-based segregation as the underlying basis for an art exhibition. Is indigenous art in Australia still in need of affirmative action and a sheltered environment for it to grow and survive? In some ways, I am more in agreement with the stance adopted by Tracey Moffatt, who, as I understand it, refuses to participate in Aboriginal-only exhibitions, claiming that a ghetto mentality is not the best way to promote Aboriginal and Torres Strait Islander art. This is reminiscent of the stance historically adopted by many women artists, for example Margaret Preston, who did not want to be included in "women only" shows; she wanted to be known primarily as an artist, who was proud to be both a woman and an Australian.

Of course, indigenous artists can and do make Australian art and in fact they make some of the best Australian art emerging from this country and this art is frequently imbued with a consciousness of country, place and identity. However, I feel that indigenous art is enhanced by being seen within the broader context of non-indigenous Australian art and it is impoverished through the loss of this more-inclusive dimension.

The curator of this exhibition, Tina Baum, relates this exhibition to the 50th anniversary of the 1967 Referendum that recognised Aboriginal and Torres Strait Islander people as Australians for the first time. The 30 invited artists have been roughly grouped into eight thematic categories: Asserting Presence; Bearing Witness; Defying Empire; Disrupting Invisibility; Forever Memory; Recounting and Revival; Resistance and Refusal, and Rising Passion. As the titles for the categories suggest, it is a politically engaged and activist exhibition, where many of the artists bear testimony to tales of horrific abuse and unthinkable denial of basic human rights. Didactic texts, slogans and simplified graphics proclaim political messages, with many of the pieces supersized, which is a strategy that we frequently associate with "biennale-style art".

Also, a conscious decision appears to have been made to integrate more traditional, tribal art, often from remote communities, with "urban indigenous" art made by artists who have been the product of modern art schools. This synthesising tendency has not been particularly successful and the exceptional subtlety of Nonggirrnga Marawili paintings with organic forms and natural pigment colours, and Rusty Peters' paintings of country clash uncomfortably with the defiant conceptual pieces of Raymond Zada or the emblematic symbolism of Archie Moore. I admire all four artists, especially Nonggirrnga Marawili's paintings on hollowed-out tree trunks, where her sensitive line-work is allowed to follow the kinks in the wood, but this collective juxtapositioning of work does little to enhance the viewing experience. The didactic message of "Disrupting Invisibility" is relevant to the artists in this section, as it is to virtually every other artist in the exhibition, but the grouping does little to bring out any potential synergies.

Defying Empire is an exhibition that brings together relatively well-known and established artists, but contains relatively few surprises. Some artists, like the high-profile artists Judy Watson and Julie Gough, produce beautiful work, but suffer through over-exposure. In contrast, Karla Dickens is brilliant and is now receiving greater recognition with a strong selection of her textile work here and possibly an even stronger selection presently on display as part of The national exhibition in Sydney. An identical comment can be made about the glasswork of Yhonnie Scarce and the installation of concrete oysters by Megan Cope: both are profound and very impressive and both presently have stronger selections on show in Sydney.

I have always had an enormous respect for the woven natural fibre work by Yvonne Koolmatrie and the pieces in this exhibition do not fail to impress, while Daniel Boyd is brilliant in his subversive history paintings. Laurie Nona's giant linocuts are impressive through scale, intricacy and somewhat quirky idiosyncratic imagery and continue in the tradition of Torres Strait Islander relief printmaking. It is interesting that a number of Torres Strait Islander printmakers are prepared to include something of themselves within the imagery – a personal as well as traditional dimension. Another Torres Strait Islander artist, Ken Thaiday Senior, from Erub (Darnley Island) in the eastern islands of the Torres Strait, is represented by his monumental masks, frequently with a funky personal touch, which never cease to amaze, surprise and challenge.

The Tiwi artist Pedro Wonaeamirri, who is well known to Canberra audiences, is a wonderfully consistent artist who sees himself as a conduit between the elders and future generations. There is a powerful determination and reserve in his art, like a beautiful cultural record that is confident in its ancestry and tradition.

When I think back to the first exhibition, Cultural warriors, it is difficult to forget the breathtaking work of John Mawurndjul, Julie Dowling and Anniebell Marrngamarrnga. The unDisclosed exhibition was unforgettable for the grand canvases of Mirdidingkingathi Juwarnda Sally Gabori and the brilliant Naata Nungurrayi. I left Defying Empire with more of a political message than memorable images. It is a message that indigenous culture is resilient, that the people despite the odds have survived and, even if they are politically and economically impoverished, in terms of visual culture, Australian indigenous artists are a superpower.

Defying Empire: 3rd National Indigenous Art Triennial, National Gallery of Australia, until September 10.