I think your statement "Once you have plasma breakeven you have a self-sustaining heater basically" is false. According to Wikipedia [1] - if I interpret it correctly - the fusion energy gain factor from plasma must be 5 (!) to have a self-sustaining heater:
"Most fusion reactions release at least some of their energy in a form that cannot be captured within the plasma, so a system at Q = 1 will cool without external heating. With typical fuels, self-heating in fusion reactors is not expected to match the external sources until at least Q = 5"