Pipewire unifies all the apis, and is fully backward compatible. It has own API too, but you don't have to use it. You can write app using any of the apis, alsa, pulse, jack, and pipewire can work with it. You only need pipewire api if you need more control or pipe through video as well.
JACK is very flexible approach to audio (think of unix pipes but audio) and this is what pipewire is inspired by, but targets the general desktop use and not just audio production as JACK does.
Generally pipewire stays out of the way and works as pulseaudio replacement, but with the pipelines you can do a lot as a power user.
Personally I think pipewire is one of the best things that has happened to linux, and since it shims all the previous audio apis instead of trying to tape the existing solutions into the package, it actually removes bloat from your system and you don't have to write weird libasound config files anymore.
JACK is very flexible approach to audio (think of unix pipes but audio) and this is what pipewire is inspired by, but targets the general desktop use and not just audio production as JACK does.
Generally pipewire stays out of the way and works as pulseaudio replacement, but with the pipelines you can do a lot as a power user.
Personally I think pipewire is one of the best things that has happened to linux, and since it shims all the previous audio apis instead of trying to tape the existing solutions into the package, it actually removes bloat from your system and you don't have to write weird libasound config files anymore.