Sabine explains the difference between nuclear fusion reaction’s Qplasma and Qtotal. There is a huge difference between the two. To put out more power than is needed to keep the reactor running, the output of the fusion reaction must be greater than Qtotal. At the rate the experiments are progressing, it will be many decades before the fusion reaction output exceeds Qtotal.
In my opinion the nuclear fusion experiments are diverting Billions of dollars from where it should be spent: on stopping climate change.