As you can see in the photos, it is hard to get a consistent or bright, well-distributed light return from step cuts, esp. emerald cuts. Something dark like tanzanite really benefits from a good pattern of light return distributed across the stone with adjacent facets winking on and off. Step cuts with a big wide keel will give you more weight for an equivalent face up area, the brilliant cuts less weight, but more brilliance. If you can find a (semi?) brilliant style cut with something of a keel, you can perhaps get some of the best of both worlds. The W^3/Vol statistic in GemCad tells you how much weight you are retaining compared to cuts of a similar width. What people are referring to in the step cuts is extinction, or areas where there is no light return. Appraisers don’t value extinction and more than 30% of it, area-wise, downgrades your gem, despite what some folks say about personal preference. In addition to the downgrade, the brilliant style cuts which throw a lot of light back face up and tilted just look better to most people. There is a reason gem cutting evolved to these. Take a look at cuts by Akhaven and Voltolini and you will see that they consistently design in this style.