So no science is not finished and yes our understanding of science still progresses. However, two things first it does not need "sceptical dissenters" to progress science. There are many areas in science where there are many "known unknowns" and where there isn't an established theory.
Moreover, even acknowledging that there are areas where "sceptical dissenters" might be right and change the established understanding, those will not come from a direction of questioning and ignoring the scientific method.
In other words someone ignores the scientific method he/she is not a legitimate dissenter.
But you need to be more specific ("butter bei die Fische" is the German expression), what are legitimate dissenters and how do you judge them as legitimate?
Are you talking about dissenters that argue by politics and own wishes? Or dissenters who have alternative explanation of history? I dont know.