Hyperfixating on producing performant code by using Rust (when you code in a very particular way) makes applications worse. Good API and system design are a lot easier when you aren't constantly having to think about memory allocations and reference counting. Rust puts that dead-center of the developer experience with pointers/ownership/Arcs/Mutexes/etc and for most webapps it just doesn't matter how memory is allocated. It's cognitive load for no reason.

The actual code running for the majority of webapps (including Lemmy) is not that complicated, you're just applying some business logic and doing CRUD operations with datastores. It's a lot more important to consider how your app interacts with your dependencies than how to get your business logic to be hyper-efficient. Your code is going to be waiting on network I/O and DB operations most of the time anyway.

Hindsight is 20/20 and I'm not faulting anyone for not thinking through a personal project, but I don't think Rust did Lemmy any favors. At the end of the day, it doesn't matter how performant your code is if you make bad design and dependency choices. Rust makes it harder to see these bad choices because you have to spend so much time in the weeds.

To be clear, I'm not shitting on Rust. I've used it for a few projects and great for apps where processing performance is important. It's just not a good choice for most webapps, you'd be far better off in a higher-level language.