Building from source, obviously, will never be really that much more performant as it mainly relies on the underlying build systems and things like ninja, cmake, cargo etc. are usually optimized very very well.
Thanks to rust just being (slightly, significantly? no idea about ruby's speed) faster + concurrent downloading & pouring of bottles, most "regular" formula installs feel a good bit faster than brew already. Mainly noticeable when installing multiple formulae at once.
Casks, especially those with pkg installers, seem to profit a bit less here.
Performance was a reason, not the main one though, like I said I wanted and still want, to build a declarative package + system managing solution on top. The idea was to get into rust with that. Imo having the base written in the same language instead of wrapping commands also gives more flexibility there.
Another reason is that I never liked the way brew looks and feels. Right now the ui/ux for Sapphire is far from finished, more like a clusterf*k and only the search command really looks the way I want it. Aiming for something modern, clean and information rich without beeing overly verbose. I really like dnf5 and what AerynOS is doing and will probably take some inspiration there.
Like mentioned, Bottles and Casks should be 100% doable and that would cover most package needs on macOS, I do not see why I should also define a new repo and packaging ecosystem when such a big and popular one exists.
Source build capability will probably stay(for easy integration of source building in the system management part later) but not be focused on brew formulae as the ruby dsl would be a horror to parse.
Well and sh*t I am not trying to compete really. This is the first time building something with rust and I really really had no idea what a giant never ending rabbit hole macOS package management is and how massive and complex Brew is.
This went from should I to can I pretty quick for me xD