Don't think I've ever seen a dart in the activewear and ballroom patterns, pitifully few though there are of the latter, but adding a dart is just what I 've been thinking of too as CarolC always used to recommend the use of darts in ballroom patterns.
Darts in lycra... I still do!
Darts and shaped seams are your friend with lycra on a body with curves. In my experience, the thing about lycra is that it wants to be gently stretched in all directions, but not too much any one way. If you pull it too hard one way, it will ripple somewhere else to compensate. Similarly, if you have to put in extra fabric (eg for a larger bust), then when you get to the edge where there is no tension, it bags. Shaped seams and/or darts allow you to control that much more easily.
If you look at big names like Chrisanne, DSI, Dore, etc dresses, for adult women they almost all use either darts or shaped princess panels (which are only darts made into seams after all) to get that smooth fit.
The brilliant DanceSportSewing patterns on Etsy are also princess panels
https://www.etsy.com/shop/DanceSportSewing (the manual that goes with those patterns is just the best thing ever, by the way!)
Here are some examples:
-- One dart (in the red) and a shaped seam where red and nude meet:
https://www.chrisanne-clover.com/en/product/new/ldd308mm_stock_collection-- Princess seams, which also make it easier to insert the godets:
https://www.chrisanne-clover.com/en/product/new/bdd207mm_stock_collection-- Darts in the bodice then panels in the skirt:
http://www.dsi-london.com/404858-emerald-ballroom-dress.html-- Princess/shaped seam over the bust, then cut away:
http://doredesigns.com/product/cherry-red-latin-with-gold-beaded-fringe-and-stonework/-- Princess seams, then a hip seam to change the skirt shape:
http://doredesigns.com/product/nude-and-white-smooth-with-ab-and-golden-shadow-stonework/Not everyone uses darts - I know Elaine Davis doesn't normally use princess seams or darts, but even she once said she will use a dart for a larger bust.
In the link you shared, if you stopped at her Step 4, you would have princess panels. You can also put some of the waist shaping into the side front seams to give a nicer line.