Yes, we're lacking context here. Most of the time developers will want to build things from scratch given the opportunity. It's simply easier (from one's opinion) and the time gap may provide with better tooling and frameworks. That applies whether the new lead developer is good or bad.

And longer time is not a good indicator too, since previously op may cutting corners to make development faster.

However 19 engineers handling one project that can be handled by one person previously is imo, a sign of not optimized work. That is, granted if the scope of work is the same for both.

IME it's a sign of one developer doing their best to get a system up and running well enough for business to get by (basically a MVP) and business not providing the staff necessary to improve upon it until it is too late. Maybe it needed 19 engineers all along. At least, that has been my experience in the past.