Actually, Dylan endorses Advanced Techs. However, this whole thing is from a misunderstanding of the development process.
For videogames, they tend to have a large development team. And that large development team is split into groups. However, I don't know how much its subdivided, it might be by roles [programmers, musicians, etc], or they could subdivide it further. In that essence, a group of people work on items, another work on character movesets, another works on Final Smashes, another work on stage design, another online, etc. However, there is limited resources in manpower, so creating final smashes would slow the development down, but not drastically. Remember how LOOONG those credit screen are.
However, I don't care for the final smashes. Might as well add them in. Most likely they will reuse Melee's engine [or parts of it] so some of the development was done the day they started. A good programmer never throws away precious code.