My personal strategy would be like those Yakuza game makers, they’ve been using the same animations, skeletons, maps, etc. ever since the first game on the ps2. But instead of scrapping everything they reuse a lot of stuff to make the process smoother, to put their focus in the gameplay and story.
To be perfectly honest if Smash just continued as a constant build on the previous iteration, I would be perfectly fine with that? I think recycling is perfectly fine in video games (especially ones with reoccurring play styles and characters like Smash). I think Ultimate is a good example of recycling done right. It’s similar, but adds enough to feel different and has a lot under its belt to make it feel full of content.
Like Mario’s alt costumes and all that? I honestly don’t believe would ever had been in a smash game built from the ground up. I think the ease that reusing assets brings is good for the long run, and it only gives us the players more content to play with.