Imo the key issues have been touched, like bolt-on props (its a fatsuit, they are kinda suposed to look heavy), too high or too low positioning (see Total body app for the maybe worst example, where Koas belly is practically all above her waist...), lack of padding adjacent areas (hips, legs mostly)...
As for Nikki19NY, there are a few of her videos showing the process and there you can see its very incremental and onion-like, with several layers of clothing and shapewear with stuffing in strategic places. The last phase of Ponzi pounds is maybe closest to this, imo one of the best fatsuits from the maxgrowth collection.
For me personally however the biggest issue is acting and story, some of the maxgrowth videos are very weak in this regard, with the good ones mostly in the past. Compare for example Fatty Godmother (obvious lack of props in latter part, but with more than enough action to make up for it), Strings Attached (worse fatsuit, but the weight is believable, the actress even knocks stuff over), The Magical Maze Mis-Adventure (star jumps anyone? short but exciting) to videos like Big Booty Bride where Lucia is just on the phone (like, really?) and at the end we graciously get one too narrow door frame. That is even before we get to the specifics like i imagine the directorial instructions "Koa, now just stand there and show me a dozen more vaguely erotical ways to touch your breasts!" or "Lucia, i want to see your most sour and annoyed face, that will be fun to watch!"
I do understand that the videos are there to appeal to the widest possible crowd, and that people like me will maybe get a few dozens of seconds at the end from them (biggest, most complete prop), not much more (but, strangely. Fatty Godmother has excellent intermediates), however it is disheartening to see for example Ludella Hahn - Snow White & The 7 Vores or The Laughing Latina - My Strange Eating Disorder , which, if you ignore the vore, feature very nice work and do some things (believability, mostly) ARGUABLY better than the expansion/fatsuit focused expert
Just my 2 cents