Rhetorical: Alma uses his experience as a bridge to the experience of his listeners. Alma was in bondage, and they too were in bondage. They were "oppressed by king Noah." The connection here is entirely spiritual.
Remember that for at least some of the time, the people willingly followed Noah (Mosiah 11:7 at least implies that they began to accept Noah's methods; Mosiah 11:17-19 has the people rejoicing after the success in the skirmish with the Lamanites, which would have appeared to give a divine stamp of approval on Noah).
The particular bondage that Alma is concerned with has nothing to do with the tax burden Noah placed on his people (see Mosiah 11:3) but with the burden of iniquity that he placed upon them. Because of the king, they were "brought into iniquity." The evil of the king was spiritual, not political nor economic. In the end, Alma's major argument against kingship is the danger of a king who turns away from God, and leads his people away from God.