I think there is no denying that, to an extend, Kuvira was a power hungry tyrant. (Though her motivations for becoming a power hungry tyrant are a little more complicated.) But that doesn't mean her rule didn't have a number of positive effects.

What you mention about improving conditions in the Earth Kingdom is a well established fact in the history of economics. Keep in mind that even at the end of Earth Queen Hou-Ting's reign the Earth Kingdom still hadn't recovered from the Hundred-Year War. (As should be obvious if you take a look at a Earth Kingdom military airship from that time.) While it were primarily Varric, Zhu Li and Bataar Beifong who brought fourth the industrialization of the whole country in the model of Zaofu, Kuvira's leadership did give the stability needed for this process.

However, we have to keep two things in mind.

First, the common citizens were not unanimously happy about it. The Earth Empire cracked down on most form of local self determination. While Kuvira kept most local governors in office, she reserved for herself the right to replace them at will, as well as the right to appoint their successors. (Not to speak of the reeducation camps. Almost every citizen knew someone who ended up in one of these.)

Second, she gambled all she had accomplished with the Invasion of Republic City. (I am veering into What-If territory a little.) Republic City was created as a compromise between the Earth Kingdom and the Fire Nation to prevent them fighting over the old Fire Nation colonies. While Fire Lord Izumi was very hesitant to intervene in the Earth Empire, she would most likely not have allowed the continued occupation of the United Republic. In other word, Kuvira almost reignited the Earth Kingdom-Fire Nation war. Which would have been disastrous for both nations.

So I would say the Earth Kingdom was lucky that Kuvira surrendered in Republic City. The people in all of the former Earth Kingdom still profit from the economy built under her and she stepped down before destroying it again.