The explanation is simple:

a) Speed - it included a lot of boring stuff, esp. in the beginning on when I was in the discovery phase and had to figure out some basics relevant for the context

b) I think I would have given up very early on, esp. of all these boring things, which are required but take long headache time to develop (e.g. The app has a somewhat complex data rendering component, containing hundres of GDI+ calls; the file is currently around 5000 lines, writing this by hand woul have taken very long and would have been very frustrating)

c) Debugging - Sometimes bugs are so deep down in some components and after 1h you stop seeing the forrest because of all single trees: The LLM can greatly help here

d) Fresh ideas: If there is a pyramid of know how in this niche, then Im currently working in "the first floor", basicly; discussions with the model about enhancing and more complex things helps to see the next island where you could swim

Yes, I could have done it without the models - but it would have taken sooo much much more time, that I wouldnt have taken the route.

Novelity: The app does one specific thing and is designed only for that specific usecase - I do not know how novel it is but since its a niche, maybe you could achieve the same thing with with existing solutions and their plugins (but then I would have had to learn how to edit/change those)

Background: 25y+ IT experience, Master degree and some other certs