Correct but John Devoy in particular and his branch of the Fenian movement were very supportive of both the land league and Parnell. The IRB/ Clan na Gael even adopted a constitution in 1879 that forbade any more attempts at insurrection without mass political support. As ever within Irish Republicanism, the problem was that militant splinter groups constantly defied the leadership on this point.It was striking that the next time Irish revolutionaries "engaged" the British Administration in the Land War, and in the Home Rule fight, the tactics used were far different.
Thanks to Parnell and Davitt, there was a broader and united "popular front" that made real gains. They ensured the transfer of the ownership of land in Ireland to the people who worked on it, and forced Ireland to the top of the agenda of British politics.
Yes, it was a very shadowy and inglorious end, as Daniel Murray explains in this article below. There were in fact two rival secret societies within the National (Free State) Army in 1924, the IRB grouped around Richard Mulcahy and the 'IRA Organisation' grouped around Liam Tobin and Charlie Dalton. The latter attempted a mutiny in protest at post Civil War demobilization, were put down by the former, but in the aftermath, Kevin O'Higgins manager to force Mulcahy's resignation from the Army and the dissolution of the IRB.Once in a casual conversation with a retired Army officer, whose career was mainly in the 1940s, told me that the IRB had a shadowy existence in the Irish Army up to his time in the force. Personal loyalty to Michael Collins and his memory was the key factor.
The "Army Mutiny" of 1924 seems to have been the turning point. Though loyal to Cosgrave, Richard Mulcahy (who led the IRB) was forced to resign as Minister for Defence, and after that secret organisations were discouraged. In a battle of politicians vs soldiers, the politicians won. It is probably that which destroyed IRB influence. An informal existence after that is not beyond the bounds of possibility, but certainly 1924 was the end of it as a force for any sort of change.
Career Conspirators: The (Mis)Adventures of Séan Ó Muirthile and the Irish Republican Brotherhood in the Free State Army, 1923-4 | The Irish Story