Project that does not need rust "Web, or IO" -> What would you actually choose to make an API then ? Python ? Ruby ? Did you compare benchmarks from rust server to python servers ? Did you actually feel the difference ?
Most web servers aren't doing anything computationally complex and there's a lot of tech to help you scale to multiple servers, so single server performance usually isn't really critical.
Web stuff is about developer speed. So familiarity, libraries, and tooling. There are plenty of good options.
Anything that needs to be performant can go in it's own service.
I will say that a rust service, even when doing relatively simple stuff, can scale well in the cloud due to small memory footprint, fast startup time when auto-scaling in containers, and no need for a JIT to "warm up" before it has high throughout and consistent low latency. Building something with these qualities on a framework like Rocket is pretty straightforward, IME.
Building a web app with rocket is like using a fine BMW to go on highway. It just feels right- I love Guards and what not he added in his framework ; absolutely refreshing work !
Web stuff is about developer speed. So familiarity, libraries, and tooling. There are plenty of good options.
Anything that needs to be performant can go in it's own service.